Because the g3 pawn isn't defended and the black king gets away.
If you had checked with your queen on h3, then the g pawn would have been defended and the next move would have been Rf1#.
Can someone tell me how this move is considered incorrect?
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I am confused when I made this move to check the black king when it said it was incorrect, I can't understand how stockfish says this is a blunder. Can someone explain?