I'm bad at this sort of thing, but you had 20. ...bf1+ rxf1 qxf1+ kg3 qxc1...that wins you a rook though I'm not sure if that's winning...maybe a draw wasn't a bad call, though certainly you could have won a bunch of material (something like ke7 and rxh8 wins back that knight. Even so, material is only even at that point.

If you were black, a win was definitely possible.  There were a lot of pieces you could have eliminated in that position with your queen.

Forgive me mosqutip, I'm a bit slow. Why wouldn't 4.h2 ward off the #?

4.Rh2 Qf1+ 5.Rg2 (only move) Qxg2#.

In addition, 17... h5 seems winning, because after you get the queen with ... Bg4+ it looks like you will be winning more material with a combination of ... Qg2 and ... Nf6+.