Badly played set?

[AmonRaa]

Party Poker No-Limit Hold'em, $0.25 BB (8 handed) Hand History Converter Tool from FlopTurnRiver.com (Format: 2+2 Forums)

SB ($3.60)
BB ($25)
UTG ($30.35)
UTG+1 ($24.15)
Hero ($21.50)
MP2 ($24.25)
CO ($4.75)
Button ($29.80)

I missed that i'm not at full buyin. Happens rarely.

Preflop: Hero is MP1 with 3[img]/images/graemlins/diamond.gif[/img], 3[img]/images/graemlins/heart.gif[/img].
<font color="#666666">1 fold</font>, <font color="#CC3333">UTG+1 raises to $0.75</font>, Hero calls $0.75, MP2 calls $0.75, <font color="#666666">4 folds</font>.

Flop: ($2.60) J[img]/images/graemlins/spade.gif[/img], 3[img]/images/graemlins/club.gif[/img], Q[img]/images/graemlins/heart.gif[/img] <font color="#0000FF">(3 players)</font>
<font color="#CC3333">UTG+1 bets $1</font>, Hero calls $1, MP2 calls $1.

Is raising here a better play?
His bet seemed weak and I kinda didnt want to loose a 3rd guy.

Turn: ($5.60) 9[img]/images/graemlins/spade.gif[/img] <font color="#0000FF">(3 players)</font>
<font color="#CC3333">UTG+1 bets $2</font>, <font color="#CC3333">Hero raises to $6</font>, MP2 folds, UTG+1 calls $4.

Time to raise it up. No more kiddie stuff :P

River: ($17.60) 6[img]/images/graemlins/heart.gif[/img] <font color="#0000FF">(2 players)</font>
UTG+1 checks, Hero bets 13$ - all in

My feeling was that if I bet 8$ he will certainly call, however it felt that I was loosing value by not maximizing profit. But is pushing maximizing profit? Any semi good player will not stack off with a pair yet he will call that 8$.

Opinions?