Did you leave that move where it was?
Did he move his King to g7?
If he did, move your queen to d5.
Your opponent will probably be overeager and try to put you into check.
Ignore it and move the king closer to the queen.
With your queen remove the pawn at b3.
If the facebook chess allows it, make your next few moves trying to get that pawn to the other side of the board, protecting it with your queen and king. If you succeed, you can promote your pawn for a second queen on the board and you'll have a much easier time of winning.
Dammit... I guess I'll have to start a game with you. Now this means I'll have to login to facebook more often.