Laydown that I regret

[CardSharpCook]

This is from a Live Limit Tourney. $550 event 55 players at the bike.

My read on Seat 2 is that he is a fish. He bets when he has stuff, he calls when he shouldn't, he plays way too many hands, and he's not that hard to read. His read on me should be that I am a tight aggressive player. He has seen me play few hands, and play those hands aggressively or get out quick.

AK [img]/images/graemlins/heart.gif[/img] [img]/images/graemlins/heart.gif[/img] in MP. Folded to me, I raise, SB (seat 2) and BB both call.

Flop: 8 [img]/images/graemlins/heart.gif[/img]6 [img]/images/graemlins/club.gif[/img]4 [img]/images/graemlins/heart.gif[/img]
SB bets, BB folds, I raise.

Turn: 8 [img]/images/graemlins/spade.gif[/img]
He checks, I check.

River: A [img]/images/graemlins/diamond.gif[/img]
He bets, I quickly raise, he just as quickly 3bets. I fold.

I'd never make this fold online, but given the read I had on him and his quick bet, I folded. I also thought, "he's got to know exactly what I have, he can't be thinking that I'd fold an ace here." But I did, and I regret it. Should I?