I like the knight sacrafice, although he declined it which I would not have done I definately think it opens up the centre in your favour either way. His knight seems in a pretty bad position to combat your push of pawns through the centre and your bishops seem perfectly poised to take full advantage of his weakened position, supported by your queen through the middle.
I should suggest his biggest mistake is to create a weakened pawn structure in the centre, particularly d6 pawn is vulnerable as is his king. He also moved his queen to a place where she can't seem to do a great deal to protect his kingside. In fact she weakens his position there because after Qb6 the capture of the knight becomes hopeless anyway due to Bxd4, Qd8 (to cover knight and move herself from the line of fire)... and then a few variations from there either way seems to get you into a winning position. With his black bishop rather stranded he didn't have enough time to use his material advantage to combat your greater deployment of position!
Not sure I can say anything else except well done, great vision! 
As a beginner and newbie on chess.com, I'd really appreciate feedback on the strengths and weaknesses of play in this game. Thanks in advance!