You did well. It was fun watching your cavalryman chase th king.
Q/N Mates are HARD (at least for me!)
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A Queen and Knight by themselves probably aren't going to force checkmate on a King that's running around in the middle of the board. Basically what you want to do is win a bunch of pawns (like you ended up doing), then try to promote a pawn (which you also attempted), while always looking out for simplification oppurtunities (ex. 38.Qxd6+ followed by trading Queens, then pushing a pawn and trading the Knight for the a-pawn.)
Watch Mr. Ed gallop around the board because I didn't know what I was doing! This was a victory, but an inefficient one: