[1/2] set vs possible overpair : maximise profit

[Varrgasss]

UTG is a quite good player, who never open-limp, especially not UTG. I put him immediately on AA/KK.

Cryptologic Network 1/2 Hold'em (6 handed) Hand History converter Courtesy of PokerZion.com

Preflop: Hero is Button with 9[img]/images/graemlins/spade.gif[/img], 9[img]/images/graemlins/diamond.gif[/img].
UTG calls, <font color="#666666">1 fold</font>, <font color="#CC3333">CO raises</font>, <font color="#CC3333">Hero 3-bets</font>, <font color="#666666">2 folds</font>, <font color="#CC3333">UTG caps</font>, CO folds, Hero calls.

Flop: (11.50 SB) 3[img]/images/graemlins/diamond.gif[/img], 9[img]/images/graemlins/heart.gif[/img], 8[img]/images/graemlins/club.gif[/img] <font color="#0000FF">(2 players)</font>
<font color="#CC3333">UTG bets</font>, <font color="#CC3333">Hero raises</font>, <font color="#CC3333">UTG 3-bets</font>, <font color="#CC3333">Hero caps</font>, UTG calls.

Turn: (9.75 BB) Q[img]/images/graemlins/club.gif[/img] <font color="#0000FF">(2 players)</font>
UTG checks, <font color="#CC3333">Hero bets</font>, UTG calls.

River: (11.75 BB) 4[img]/images/graemlins/spade.gif[/img] <font color="#0000FF">(2 players)</font>
UTG checks, <font color="#CC3333">Hero bets</font>, UTG calls.

Final Pot: 13.75 BB


I think my biggest mistake is on the flop : i shouldnt cap because UTG now suspects i have him beat and check-calls to the river. I should just call his 3bet right ?
What would then be the perfect line on the turn (if i called his 3bet on the flop) ? Raise or just call to raise river ?

Other question : my 3bet PF is bad too right ? Since i am almost sure that UTG holds AA/KK, i know i only play for a set and i should just overcall CO's raise (thinking he will call UTG's 3bet) and so maximise my profit if i hit ?
Thank you for your advices [img]/images/graemlins/wink.gif[/img]