Comments on turn? Should I have called the raise instead of 3-betting it since I was obviously beat?

Party Poker 0.50/1.00 Hold'em <font color="#0000FF">(10 handed)</font> link

Preflop: Hero is MP1 with A[img]/images/graemlins/spade.gif[/img], 2[img]/images/graemlins/spade.gif[/img].
UTG calls, <font color="#666666">2 folds</font>, Hero calls, MP2 calls, MP3 calls, CO calls, Button calls, SB completes, BB checks.

Flop: (8.00 SB) 7[img]/images/graemlins/spade.gif[/img], 6[img]/images/graemlins/heart.gif[/img], 9[img]/images/graemlins/spade.gif[/img] <font color="#0000FF">(8 players)</font>
SB checks, BB checks, UTG checks, Hero checks, <font color="#CC3333">MP2 bets</font>, MP3 calls, <font color="#CC3333">CO raises</font>, Button folds, SB folds, BB folds, UTG folds, Hero calls, MP2 calls, MP3 calls.

Turn: (8.00 BB) A[img]/images/graemlins/diamond.gif[/img] <font color="#0000FF">(4 players)</font>
<font color="#CC3333">Hero bets</font>, MP2 calls, <font color="#CC3333">MP3 is all-in ($0.75)</font>, <font color="#CC3333">CO raises</font>, <font color="#CC3333">Hero 3-bets</font>, MP2 folds, <font color="#CC3333">CO caps</font>, Hero calls.

River: (17.75 BB) Q[img]/images/graemlins/club.gif[/img] <font color="#0000FF">(3 players, 1 all-in)</font>
Hero checks, <font color="#CC3333">CO bets</font>, Hero calls.

Final Pot: 19.75 BB.