AK hitting nothing

[inferno]

I feel like I have put to much money in with nothing, how is this hand played? Should I fire again on the turn?

Full Tilt Poker $0.50/$1 No Limit Hold'em - 6 players
Hand Converter Tool from DeucesCracked.com

SB: $99.00
BB: $30.55
UTG: $24.80
MP: $104.20
CO: $98.50
Button: $108.95

Preflop: Hero is SB with A[img]/images/graemlins/club.gif[/img], K[img]/images/graemlins/club.gif[/img]
UTG folds, MP folds, CO calls $1, <font color="#FF0000">Button raises to $4.50</font>, <font color="#FF0000">Hero raises to $12</font>, BB folds, CO folds, Button calls $7.50.

Flop: ($26.00) 5[img]/images/graemlins/spade.gif[/img], 5[img]/images/graemlins/heart.gif[/img], 9[img]/images/graemlins/heart.gif[/img] <font color="#0000FF">(2 players)</font>
<font color="#FF0000">Hero bets $20</font>, Button calls $20.

Turn: ($66.00) 7[img]/images/graemlins/spade.gif[/img] <font color="#0000FF">(2 players)</font>
Hero checks, Button checks.

River: ($66.00) 7[img]/images/graemlins/club.gif[/img] <font color="#0000FF">(2 players)</font>
Hero checks, <font color="#FF0000">Button bets $42</font>, Hero folds.

Final Pot: $66.00