2...g6? ; lets him grab the pawn, I usually play d6, Nf6 is also playable.
4...f6? ; weakens the kingside. Better would have been Nf6 then Nc6 to give the queen the boot.
8...Nge7? ; Bxb4 would have regained your lost pawn.
9...Qe5! ; good move.
11...Qd6??; 11...Nxc4 12. Nxe5 Nxe5 and you are comfortably ahead.
12...Qf4? ; your queen is not safe there, as you soon shall see.
13...Bg7??? ; hangs your queen.
19. Qc3??? ; gives the queen and the game back. You got lucky.
I've never seen this before. Probably played it totally wrong, but for some reason he resigned once I took his queen... finally.