Re-raised Pots : Big Leak

[Fight Club]

Villan is StopLose, semi Lag 27/22/2, hasn't got out of line from what i've seen.

Party Poker No-Limit Hold'em, $ Hero (5 handed) Hand History Converter Tool from FlopTurnRiver.com (Format: 2+2 Forums)

SB ($815)
Hero ($1000)
UTG ($1334)
MP ($1112.50)
Button ($1142.50)

Preflop: Hero is BB with K[img]/images/graemlins/heart.gif[/img], A[img]/images/graemlins/club.gif[/img]. SB posts a blind of $5.
<font color="#666666">1 fold</font>, <font color="#CC3333">MP raises to $33</font>, <font color="#666666">2 folds</font>, <font color="#CC3333">Hero raises to $123</font>, MP calls $100.

Flop: ($271) 6[img]/images/graemlins/spade.gif[/img], A[img]/images/graemlins/diamond.gif[/img], 8[img]/images/graemlins/club.gif[/img] <font color="#0000FF">(2 players)</font>
<font color="#CC3333">Hero bets $125</font>, MP calls $125.

Turn: ($521) 5[img]/images/graemlins/diamond.gif[/img] <font color="#0000FF">(2 players)</font>
Hero checks, MP checks.

River: ($521) Q[img]/images/graemlins/diamond.gif[/img] <font color="#0000FF">(2 players)</font>
<font color="#CC3333">Hero bets $255</font>, MP pushes

I usually bet this stronger and probably should have because I'm sure he's capable of bluffing the river. I think he's most often got QQ/AQ/88-1010/air here. The main reason for betting small was to get value from underpairs, not to induce a bluff.

Looking back I hate my river bet, any ideas for the river as played?