In a casual blitz game I had with my friend, my last move was to promote a pawn, to ladder mate my opponent (there was already a rook on the 7th). I moved the pawn, but while I was reaching for the queen I ran out of time. Who won?
Nobody won. It was a draw.
According to the FIDE Laws of Chess:
Except where one of Articles 5.1.1, 5.1.2, 5.2.1, 5.2.2, 5.2.3 applies, if a player does not complete the prescribed number of moves in the allotted time, the game is lost by that player. However, the game is drawn if the position is such that the opponent cannot checkmate the player’s king by any possible series of legal moves.
You haven't completed your move by placing a queen on the board and pressing your clock so this applies to your situation. However you have got far enough through making your move that you are committed the pawn and giving checkmate. That means that your "opponent cannot checkmate the player’s king by any possible series of legal moves". That in turn means that the game is a draw.