help me find mate

At the end of this game, I was up with a rook, 2 bishops & 2 pawns. My opponent only had a rook and was able to gain a stalemate. This might have been my best win. I know a checkmate was possible but couldn't figure it out. Where did I go wrong? What could I have done differently?

I think that 55.Bg5 would have give you the perfect move for a checkmate net