[NL100] Small overpair gets 3bet all in on flop

[Ranma4703]

Villain is dumb like a brick, but not super aggro or anything. I haven't been making too many waves, and I've been playing pretty tight. I doubt he has noticed. Stack sizes are 57$.
He raises UTG to $3.50, I call in the c/o with 99. Flop comes out:
8 [img]/images/graemlins/diamond.gif[/img]2 [img]/images/graemlins/heart.gif[/img]3 [img]/images/graemlins/club.gif[/img]
He bets out 1/2 pot (4.50$), I raise to 12$ because I'm pretty sure he has air and I don't want a J, Q, K, or A coming off. He instapushes. Standard fold?