Im not very good, but I thought I noticed something 'strange'.
You played: 12. a3, but what is wrong with 12. Ne5 threatening to eat the bishop? The pawn cant take the knight because it is pinned to the Queen. The bishop cant eat your pawn because the Queen will eat it. The bishop only has one retreat square: e8. So:
12. Ne5 Be8 13. a3 Nc6 14. Nxc6 Bxc6 15. e5
And you are winning all over the place.