50NL AA Did I play this too passivly?

[dimeetrees]

Full Tilt Poker No-Limit Hold'em, $0.50 BB (6 handed) Hand History converter Courtesy of PokerZion.com

Button ($20.20)
SB ($9.70)
BB ($69.35)
UTG ($50)
Hero ($52.10)
CO ($57.05)

Preflop: Hero is MP with A[img]/images/graemlins/club.gif[/img], A[img]/images/graemlins/heart.gif[/img].
UTG calls $0.50, <font color="#CC3333">Hero raises to $2.25</font>, <font color="#666666">4 folds</font>, UTG calls $1.75.

Flop: ($5.25) 8[img]/images/graemlins/heart.gif[/img], 9[img]/images/graemlins/club.gif[/img], 7[img]/images/graemlins/spade.gif[/img] <font color="#0000FF">(2 players)</font>
UTG checks, <font color="#CC3333">Hero bets $5</font>, UTG calls $5.

Turn: ($15.25) 4[img]/images/graemlins/heart.gif[/img] <font color="#0000FF">(2 players)</font>
UTG checks, Hero checks.

River: ($15.25) J[img]/images/graemlins/diamond.gif[/img] <font color="#0000FF">(2 players)</font>
<font color="#CC3333">UTG bets $15.25</font>, Hero folds.

Final Pot: $30.50

no reads on opponent. In hindsight, i should have probably bet the turn and put my opponent on a streight draw, but at the same time I felt like that board hit a lot of hands and that I should keep the pot small and call a reasonable bet on the river.