Middle Flush

[Ringo_Mojo]

Party Poker 1/2 Hold'em (10 handed) converter

Preflop: Hero is SB with 5[img]/images/graemlins/heart.gif[/img], 9[img]/images/graemlins/heart.gif[/img]. CO posts a blind of $1.
<font color="#666666">3 folds</font>, MP1 calls, <font color="#666666">2 folds</font>, CO (poster) checks, Button calls, Hero completes, BB checks.

Flop: (5 SB) J[img]/images/graemlins/heart.gif[/img], 6[img]/images/graemlins/heart.gif[/img], 5[img]/images/graemlins/club.gif[/img] <font color="#0000FF">(5 players)</font>
Hero checks, <font color="#CC3333">BB bets</font>, MP1 calls, CO calls, Button folds, Hero calls.

Turn: (4.50 BB) 3[img]/images/graemlins/heart.gif[/img] <font color="#0000FF">(4 players)</font>
Hero checks, <font color="#CC3333">BB bets</font>, MP1 calls, CO calls, <font color="#CC3333">Hero raises</font>, MP1 calls, CO folds, Hero calls.

River: (11.50 BB) 9[img]/images/graemlins/spade.gif[/img] <font color="#0000FF">(3 players)</font>
Hero checks, <font color="#CC3333">MP1 bets</font>, Hero calls.

Final Pot: 13.50 BB

I've only been playing for a couple months, and I'm trying to improve my game. This hand kinda confused me. I have a midle flush on the turn, but slowed down on the river for fear of a bigger flush. Should I have played this differently? what type of odds are there for an opponent to have a bigger flush in this situation?