It's just not right to slowplay with an overpair.

Go read SSHE on slowplaying. You should only be slowplaying when you think your opponents can only improve to second best behind you. Given the way the hand played, with a Q and a 2 flush on the board, that just wasn't the case.

Pop the flop and try to clean up the aces and gutshots as explained by Nick. You'd be kicking yourself had you not caught that miracle river card.