PF action? Blinds? Why is villian on an overpair? Is your 68 suited or not (either way vs an overpair to you and the board makes you about 2 to 1, but one way is just over 2 to 1, the other is just under 2 to 1).
Based on what we know...I assume worst case he's on an overpair and your 68 is unsuited. If so, then it like 2.1 against you to win. So even if he had shoved his $6 into the $8.75 pot, you'd have had the correct pot odds
(2.5ish to 1) to call. Personally I would reraise him all-in for his last $3. If we're wrong on his holding, he might (incorrectly) fold. And even if he does call with that overpair, the play looks to be +ev (heh, or am I just that tired? ).