Where to fold top pair?

[no1spec]

This felt like I was spewing calling down.
Did I go to far on flop?
What is the best line here?

Party Poker 0.50/1 Hold'em (6 handed) FTR converter on zerodivide.cx

Preflop: Hero is BB with A[img]/images/graemlins/heart.gif[/img], 9[img]/images/graemlins/spade.gif[/img].
<font color="#666666">2 folds</font>, CO calls, <font color="#666666">1 fold</font>, SB completes, Hero checks.

Flop: (3 SB) 7[img]/images/graemlins/heart.gif[/img], A[img]/images/graemlins/spade.gif[/img], 4[img]/images/graemlins/diamond.gif[/img] <font color="#0000FF">(3 players)</font>
SB checks, <font color="#CC3333">Hero bets</font>, <font color="#CC3333">CO raises</font>, SB folds, <font color="#CC3333">Hero 3-bets</font>, <font color="#CC3333">CO caps</font>, Hero calls.

Turn: (5.50 BB) 3[img]/images/graemlins/club.gif[/img] <font color="#0000FF">(2 players)</font>
Hero checks, <font color="#CC3333">CO bets</font>, Hero calls.

River: (7.50 BB) T[img]/images/graemlins/diamond.gif[/img] <font color="#0000FF">(2 players)</font>
Hero checks, <font color="#CC3333">CO bets</font>, Hero calls.

Final Pot: 9.50 BB