Is there someone kind enough who can help me analyse this game ????

I played a game against a player rated ~2000. I'm currently near 1620. Can someone please help me on realising me my mistakes? I played as black

you didn't castle. you accepted a gambit pawn then lost more tempos with your knight trying to chase down the bishop.

if you think it is not an easy task, just tell me a little about opening inaccuracies... please?

I've never seen 3. Be7. Looks weird, because it takes away a potential square for your knight. I suppose you already know Bc5 is the normal move there. But I guess given that, 4. ...d3, or 4. ...dxc3, followed by 5. d6, then Nf6, then ...0-0? Honestly it looks awkward after 3. ...Be7, but maybe it's playable.

sorry got some move numbers wrong; typing on the phone. But hopefully you get the idea.

I think 5... Na5 is bad.

Yeah, you pretty much got nailed by the pawn gambit. Your opponent did a good job with active play and catching your king in the center of the board in an open position.

In these gambit positions, you have to seriously consider giving back the pawn you won if it means castling to safety. Like instead of 15.Rc8 to hang onto your material, 0-0, and letting him play Bxc7 winnign his pawn back.

Chasing down the enemy bishop earlier on was probably an inaccuracy as well.

But for sure, the root of your quick demise was getting your k trapped in the center, which is actually often the whole point of gambit lines like this one and the not-too dissimilar Smith Morra gambit, where you sac pawns and even pieces to get a big attack on the uncastled king. 

I suspect a computer can show you lines where you can in fact take and keep the pawn, but a lot of these gambit lines are considered dangerous enough even by grandmasters (like the Smith Morra gambit for the sicilian) that they often shy away from keeping the gambited pawn.

because of 6.Bxf7+!? Kxf7 7.Qh5+ regaining the piece and your king is vulnerable.

My bad... 😂 board blindness. Sorry. Qh5+ is out of the question. !!

3... Be7 is an accepted (Hungarian, I believe) variation, but ...Bc5 is normal because it slows down the desirable advance d4 for White.

5... Na5 is decentralizing and a waste of time. I personally advocate acceptance of the gambit followed by 6...d6, development and quick castling.

After White castled, all he needed to do was blow open the center and the rest flowed naturally. Castling short on move 14, as mentioned before looks safer for black - jettisoning the extra pawn for a safe King. Black would still have a rather unpleasant position in my opinion, but at least he can fight back. White's rejoinder 15 Ba6 sealed the game I think. And the loss of the Queen on move 20 essentially ended all resistance.

To be honest, this sort of swift and deadly attack has always soured me on the open games, but they definitely help to illustrate how important development can be in certain positions.

Well Here is what i found.

Be7?1 - a Bit too passive. Sharper was Bc5. Remember We should keep our pieces on the center

Na5?1 - Moving the Same piece twice

dxe5? - Altho this looks fine but keeping the Tension up is the way to go

After Looking at this game i found out that:

Strategy and Calculation are your weakest points.

So Work On strategy(especially your thinking system) and Your Calculation System.

BTW send me your email in private message. I will send you the resources for training.

I like how you put a game you lost to analyze. Everyone else puts a game they won to analyze to make them feel good. This shows you truly put this game up to learn and get better.