Flopped a set, but staight and flush draws come on turn/river

Hello all,

Comments welcome on all streets.

Party Poker No-Limit Hold'em, $ BB (9 handed) FTR converter on zerodivide.cx

Hero ($50)
MP3 ($45.63)
CO ($116.63)
Button ($45.36)
SB ($47)
BB ($38.25)
UTG ($51.05)
UTG+1 ($42.62)
MP1 ($48.75)

Preflop: Hero is MP2 with 7[img]/images/graemlins/spade.gif[/img], 7[img]/images/graemlins/diamond.gif[/img]. SB posts a blind of $0.25.
<font color="#666666">1 fold</font>, UTG+1 calls $0.50, <font color="#666666">1 fold</font>, Hero calls $0.50, <font color="#CC3333">MP3 raises to $1</font>, <font color="#666666">1 fold</font>, Button calls $1, <font color="#666666">1 fold</font>, BB calls $0.50, UTG+1 calls $0.50, Hero calls $0.50.

Flop: ($5.25) 6[img]/images/graemlins/club.gif[/img], 8[img]/images/graemlins/spade.gif[/img], 7[img]/images/graemlins/heart.gif[/img] <font color="#0000FF">(5 players)</font>
BB checks, UTG+1 checks, <font color="#CC3333">Hero bets $3</font>, MP3 folds, Button folds, BB calls $3, UTG+1 folds.

Turn: ($11.25) 2[img]/images/graemlins/club.gif[/img] <font color="#0000FF">(2 players)</font>
BB checks, <font color="#CC3333">Hero bets $6</font>, <font color="#CC3333">BB raises to $12</font>, Hero calls $6.

River: ($35.25) 4[img]/images/graemlins/club.gif[/img] <font color="#0000FF">(2 players)</font>
<font color="#CC3333">BB bets $15</font>, Hero folds.

Final Pot: $50.25

-Grant