After White 40th move=Knight captured f3.You should of move your Rook=Rg6 Check.After a couple of more moves.=You could of been a Queen up.

After

37... Ka8 your oppent could play

38. Qg8+ (threatning Qb8#)

So you had to play

38 ... Rf8

39. Kxg8

With a lot of chances to defence after Qxg7, and some perspective to attack, cause after Kd7 the threat of mate on b8 could be renewed.

But yours chances were still higher.

Well there's a lot of mistakes from both sides, as always in chess)

Was it a blitz game? 

16… Qd7 seemed to be a bit of a blunder because 17. Be6 put a lot of pressure on a cramped position.

However after castling and with the White Queen on h3 I was able to activate my pieces into stronger positions