Flop good or bad?

[Cactus Jack]

PokerStars No-Limit Hold'em Tourney, Big Blind is t150 (8 handed) FTR converter on zerodivide.cx

BB (t2285)
UTG (t1920)
UTG+1 (t2995)
MP1 (t1030)
MP2 (t710)
Hero (t2555)
Button (t2115)
SB (t1290)

Preflop: Hero is CO with A[img]/images/graemlins/club.gif[/img], 5[img]/images/graemlins/club.gif[/img].
UTG calls t150, UTG+1 calls t150, <font color="#666666">2 folds</font>, Hero calls t150, Button calls t150, SB completes, BB checks.

Flop: (t900) 5[img]/images/graemlins/heart.gif[/img], 5[img]/images/graemlins/spade.gif[/img], 8[img]/images/graemlins/spade.gif[/img] <font color="#0000FF">(6 players)</font>
SB checks, <font color="#CC3333">BB bets t300</font>, UTG folds, UTG+1 folds, Hero calls t300, Button calls t300, SB folds.

Turn: (t1800) 4[img]/images/graemlins/spade.gif[/img] <font color="#0000FF">(3 players)</font>
BB checks, <font color="#CC3333">Hero bets t300</font>, Button calls t300, BB calls t300.

River: (t2700) T[img]/images/graemlins/diamond.gif[/img] <font color="#0000FF">(3 players)</font>
BB checks, Hero checks, Button checks.

Final Pot: t2700

Results in white below: <font color="#FFFFFF">
BB has 5d 7d (three of a kind, fives).
Hero has Ac 5c (three of a kind, fives).
Button has 7s 6c (straight, eight high).
Outcome: Button wins t2700. </font>

I'm at sea with this hand. How should I have played it?