Flopped a set... should I fold it?

Going from memory...

Hero (UTG) $25 ---- dealt 6/6
Villian #1 (CO) $15
Villian #2 (Button) $15

I limp, so does most everyone else, 8 guys see the flop:

Flop: 5[img]/images/graemlins/heart.gif[/img] 6[img]/images/graemlins/heart.gif[/img] 7[img]/images/graemlins/spade.gif[/img] ($2 in pot)

Checked to me
Hero bets $3.
Folds around to CO
CO calls $3.
Button calls $3.

Turn: 9 [img]/images/graemlins/diamond.gif[/img] ($11 in pot)
Hero checks.
CO bets $6.
Button calls.
Hero..... ?