Missed value bet? - hand w/ 2+2er

[Octopus]

MP3 is cnfuzzd. I do not know if he recognized my screen name, but he probably could guess my early limping standards fairly accurately.

Party Poker 3/6 Hold'em (9 handed) converter

Preflop: Hero is MP1 with A[img]/images/graemlins/heart.gif[/img], 2[img]/images/graemlins/heart.gif[/img].
<font color="666666">2 folds</font>, Hero calls, <font color="666666">1 fold</font>, <font color="CC3333">MP3 raises</font>, <font color="666666">4 folds</font>, Hero calls.

Flop: (5.33 SB) 6[img]/images/graemlins/heart.gif[/img], 7[img]/images/graemlins/club.gif[/img], 2[img]/images/graemlins/diamond.gif[/img] <font color="blue">(2 players)</font>
<font color="CC3333">Hero bets</font>, <font color="CC3333">MP3 raises</font>, Hero calls.

...No flush draw. No way he has a straight draw. I seriously doubt a set. I seriously doubt top (or middle) pair. So, it is either overcards or an overpair. That is, I am ahead to 3 or 6 outs or behind to 5 (or 2) outs.

Turn: (4.66 BB) 3[img]/images/graemlins/spade.gif[/img] <font color="blue">(2 players)</font>
Hero checks, MP3 checks.

...At this point, I strongly believe it is overcards.

River: (4.66 BB) Q[img]/images/graemlins/heart.gif[/img] <font color="blue">(2 players)</font>
Hero checks, ...

...Here is where I wimp out. At the table, I started wondering if he would call me with a worse hand. With a better hand he would probably raise me, but he might do that even without, so I probably can't fold to a raise. I also thought perhaps he might take another shot at the pot with AK or AJ since I had checked twice. Opinions? (Or am I way overthinking this?)