flopped the nut flush. How was my betting?

[DrewOnTilt]

Hi all! I am getting the hang of tourneys but am still working on proper betting. I flopped a monster here. The table was fairly loose/passive and I didn't want to overbet and scare people out. How'd I do? Should I have bet stronger? BTW on the flop I was going for the check-raise but nobody opened.

Party Poker No-Limit Hold'em Tourney, Big Blind is t15 (9 handed) converter (http://www.selachian.com/tools/bisonconverter/hhconverter.cgi)

UTG+1 (t760)
MP1 (t490)
MP2 (t540)
MP3 (t530)
CO (t1240)
Button (t880)
SB (t1685)
Hero (t725)
UTG (t1150)

Preflop: Hero is BB with K/images/graemlins/diamond.gif, J/images/graemlins/diamond.gif.
UTG calls t15, UTG+1 folds, MP1 calls t15, MP2 folds, MP3 folds, CO calls t15, Button folds, SB completes, Hero checks.

Flop: (t75) 9/images/graemlins/diamond.gif, 3/images/graemlins/diamond.gif, A/images/graemlins/diamond.gif <font color="blue">(5 players) </font>
SB checks, Hero checks, UTG checks, MP1 checks, CO checks.

Turn: (t75) K/images/graemlins/heart.gif <font color="blue">(5 players) </font>
SB checks, <font color="CC3333">Hero bets t50</font>, UTG folds, MP1 calls t50, CO folds, SB folds.

River: (t175) 3/images/graemlins/club.gif <font color="blue">(2 players) </font>
<font color="CC3333">Hero bets t175</font>, MP1 calls t175.

Final Pot: t525
<font color="#990066">Main Pot: t525 (t525), between MP1 and Hero.</font> &gt; <font color="white">Pot won by Hero (t525).</font>

Results:
Hero shows Kd Jd (flush, ace high).
MP1 shows As 9c (two pair, aces and nines).
Outcome: Hero wins t525.