Why is my rating so low

Right off the bat the first thing that I noticed was white missing 27.Qg7#.  I'm surprised that you didn't play 25.Nxb2 removing that threat that was telegraphed.

Also, on move 2, play 2...Nc6.  Threats like 2.Qh5 are easy to defend against by developing your pieces naturally. While 2...Qf6 defends the e-pawn, it gets in the way of placing the king knight on one of its best squares in f6 and removes a potential support piece of a d5 pawn push.  You need  to try and play against stronger competition who don't rely on threats like this.

My usual move is to develop the knight with an attack on the queen, then block check with the bishop when the queen takes pawn. Then I threaten the queen on the next move bringing out my other knight. This actually hasn't usually ended well for me so I don't do it anymore lol.

Im not sure if he ignored it, he just prefered to use the time and attack. In this case he was right because 27. Qg7 is simply checkmate. Again I would spend more time improving your pieces and less time attacking with one piece. Why 25. Pxe3? The knight is in a nice position here. Meanwhile your other knight, your bishop and your second rook are completely out of the game. Instead of a meaningless attack with the knight you could have just improved one of the other pieces.
I would suggest going over the game and looking for moves where you worsened the position. for example ask yourself how your Knight ended on the horrible a6 and what you could have done to prevent it. Maybe you can post an annotated version of this game where you highlight what you think was wrong with certain moves and what could be a better alternative.

You would be down a piece but have a tempo advantage. But I would recommend Nc6 as lostpawn said. if he doesnt move the queen you can simply play Nf6 next and you gain a tempo.

That's what I was saying I usually do lol. For some reason it generally doesn't end well. I think I spend too much time attacking the queen after Nf6, where I'd be better off continuing development once he moves his queen.

I've seen that so many times I know a few different variations four or five moves deep off the top of my head lol. And I know it's the "queen attack, kiddie countergambit" lol.

Use the pieces like an orchestra... make them sing.

Opening principles exist to guide your moves at the beginning of a game.

1) Make moves that occupy or control the central squares at the beginning of a game.  By focusing your pieces and pawns on the central squares, you give yourself the most options to develop as the game proceeds.

2) Don't move the same piece multiple times in the opening.  While there are exceptions to this rule, following this principle ensures that you develop your pieces quickly and are able to seize the initiative quicker.

3) Try not to bring your queen out early in the game. The majority of this time, the threat that the queen provides is minimal and gives the opponent an easy target to develop pieces and seize the initiative at the same time.

4) Get your king to safety as quickly as possible.  Keeping your king in the center or making weakening pawn moves, gives your opponent an easy target to attack.  By castling quickly and not being quick to move pawns that will open up lines to your king,  you are more likely to keep your king safe and stay in the game longer.

Yes, we Know.

This all sounds great in theory but I actually got stuck at 650 doing stuff like this mindlessly. For whatever reason, the 800 players on here are good enough that you need to do more than just follow basic opening principles.

Yes, many player here are surprisingly good... 16k blitz here is a tough game.

"This all sounds great in theory but I actually got stuck at 650 doing stuff like this mindlessly. For whatever reason, the 800 players on here are good enough that you need to do more than just follow basic opening principles."

No... they aren't.  How many times have you played games where the queen is brought out on the second move?  How often do you play or have to defend against quick mating attacks?  How often do you or your opponents play moves like pawn to f3 or f6 which creates kingside weaknesses and slows down development?  How often do you or your opponent play moves like Bd3 or Bd6 blocking central pawns and hindering development?  Playing moves and exhibiting behaviors like what I've listed above and not following proven principles on how to start off a chess game is truly playing mindlessly.

Using principles to guide your play isn't playing mindlessly.  It is being mindful of the best way to start a game and being able to quickly take advantage of mistakes your opponent makes (Like 7...f6).  Using principles to guide your play will help you avoid making bad moves in the opening (Like 7...f6) and will speed up the process of recognizing and taking advantage of bad moves (Opening up the e-file, keeping your king in the center, and sacrificing a pieces to remove the only piece defending your king) that your opponent makes.

Yuh huh, Kool Aid again?

What's the opening principle I failed to follow here then?

The analysis shows that I made a single mistake against an 850 rated player and lost down a piece.

Don't know, but I think some common second-move choices are 2 Nf3, 2 c3, and 2 Nc3.

#kthprog

Well done! Other than a few unfortunate moves (including allowing a mate in one and allowing a knight to be captured), I can see the effort that you have put in.

We usually try not to make moves like 7...Nbd4. It is a great idea to attack the c3 pawn, but this blow is easily defendable (White: Hmmm...why is he moving the knight there? Oh...attacking the c2 square!) and eventually the knight did move back afterwards.

On move 25, the idea 25...Nxb2 eliminates strong attacks coming from the diagonal. Often, that diagonal is a source of trouble for a kingside castled Black king.

Maybe your opponent 'mouse-slipped' on move 27? It's possible to mouse-slip at this point.

Well done on spotting something on move 35! Simplification reduces chances of Black getting checkmated because now the queens are off the board. It is noteworthy that the other move order, 35...Bh3, is equally good. In any case, being two pieces up at this point, any move that does not allow immediate mate or lose pieces should win.

1. Buy a book.

2. Stop playing online games for a bit. Play a computer. I know this sounds weird, but computers won't make as many mistakes, so you start learning to look for solid moves over sneaky moves.

3. Watch videos from Saint Louis chess club, agadmator's analysis games, or really any chess videos. Watching people explain grandmaster games is really beneficial.

4. Slow down. I don't know if you are, but this really helped me.

Good luck!

Good advising... simple act of slowing down a little got me from 14k to 16k... you don't need to play super slow... but when you learn not to rush, the game become a lot easier?! Play some longer games... so you relax a little more.

OP, did you say you have 2 accounts ? As I understand it, that is not permitted on chess.com