What did I do wrong?

You made a great amount of mistakes. Your greatest mistake was probably deciding not to concentrate.

Well first off all your comments made me laugh, I appeciate that. Looks like you had fun despite losing and that's important. I am no expert by far but here's a couple things I noticed.

Opening play was sloppy in general, key rules are to develop pieces (i think they say no more than 2 pawn moves in the first 5-10 or something), control the center, and prepare to castle. (May want to study one specific opening and get really good at it. If you like to play white and open with e4, check out the Ruy Lopez. Strong opening and great for beginners.)

You lost your right to castle when he ate your queen. Sure material was even when you recaptured, but this is a big loss for you. Should not have taken his pawn anyway as your middle pawn is better than his side pawn (remember control the center). I would just continue to develop your pieces with Nc3 or Be3 if you want to protect the pawn. But really you can just attack with your Knight if he takes your pawn.

At move 13 you saved your rook, but then gave it back up the next turn. Now occasionally a piece in a certain can be worth more or less but I'm not good enough to tell you that, so I just follow (and recommend the same to you) the standard point rules. Rook is worth 5 while Knights only worth 3. Let him have the Knight instead.

At move 17 you talk about resigning.... he's only up by about a piece (Knight/Bishop ~ 3 points), which is 1 mistake on his part, so it's overcomeable. What your real losing signal at this point is that he has 3 active pieces and you have 1. You literally still have both bishops and your rook on their starting squares and havn't moved any of them even once.

Thanks! And since it wasn't a real tournament, and I am a begginner, it doesn't matter to me if I win or lose. Also, I've only been serious about chess for the last few months.

my advice would be to go to chesstempo and do about 10-20 puzzles per day or buy a tactics book after three months of tactical training you should be about 1400-1500 here

"Two knights better than one... Unless otherone was eaten" rofl

That must be the best annotation I've ever read. :D

Move 6 Dxc5 created a perminant weakness as you lost the ability to castle and the center is already open. The queens are off the board so you may have been able to recover. Perhaps developing a knight would have been a better idea.

Move 8 b3 with the idea of fianchetto your bishop would have worked better than b4, you tried to hang onto that pawn that was a bad idea costing you the exchange.

After around move 13... 0-0-0+ your position is resignable. if not sooner. Anything after that just picture yourself fighting with a broken leg and your opponent is just leaning on you the entire time until you fall over.

Protect your king better, focus more on developing pieces towards the center and you will improve.