Big pot - overcall or fold here?

[RobMay]

This hand makes me look like a calling station who makes the worst poker mistake ever on the river!

Party Poker 0.5/1 Hold'em (10 handed) converter

Preflop: Hero is MP3 with J[img]/images/graemlins/spade.gif[/img], K[img]/images/graemlins/spade.gif[/img]. CO posts a blind of $0.5.
UTG calls, <font color="#CC3333">UTG+1 raises</font>, <font color="#666666">3 folds</font>, Hero calls, <font color="#666666">3 folds</font>, BB calls, UTG calls.
(I would have raised, but UTG+1 got there first, so I called and hoped for a few more loose calls behind me)

Flop: (9.50 SB) 6[img]/images/graemlins/heart.gif[/img], Q[img]/images/graemlins/spade.gif[/img], J[img]/images/graemlins/club.gif[/img] <font color="#0000FF">(4 players)</font>
BB checks, <font color="#CC3333">UTG bets</font>, UTG+1 calls, Hero calls, <font color="#CC3333">BB raises</font>, UTG calls, UTG+1 calls, Hero calls.
(Again, I'd normally bet or raise this pair/backdoor flush, but with 2 out of 3 opponents already in I didn't see any point in trying to isolate the last guy - I acknowledge this mistake!)

Turn: (8.75 BB) 4[img]/images/graemlins/spade.gif[/img] <font color="#0000FF">(4 players)</font>
<font color="#CC3333">BB bets</font>, UTG folds, UTG+1 calls, Hero calls.
(No equity in raising my draw against 2 opponents, so another boring call ...)

River: (11.75 BB) 4[img]/images/graemlins/diamond.gif[/img] <font color="#0000FF">(3 players)</font>
<font color="#CC3333">BB bets</font>, UTG+1 calls, Hero folds.
(I KNOW you're not supposed to fold for one bet in a large pot unless you're ABSOLUTELY SURE you're beat ... but against a bet by the flop raiser as well as a call by the other guy (who can't be bluffing, right?) I really thought I had no chance.

Final Pot: 13.75 BB

Results in white below: <font color="#FFFFFF">
BB has 3c 6c (two pair, sixes and fours).
UTG+1 has Ah Kd (one pair, fours).
Outcome: BB wins 13.75 BB. </font>

I felt like the initiative had already been taken away from me before my first decision, so by calling as cheaply as I could I only spent 3BB on this hand ... or did I miss out on a 13.75BB pot by playing weak?