Hand help

I'm not an experienced player and thought villain was bluffing on the river :- but was my bet sizing wrong here?

NL Texas Hold'em $55 Buy-in + $5 Entry Fee, Level:1 Blinds(10/20-(no ante)) - Tuesday, January 26, 20:15:08 GMT 2010
*HOT! Stack Up $12,000 GTD Freezeout #334110
Table 1 9-max (Real Money)
Seat 8 is the button
Total number of active players : 9
Seat 1: barry04 ( 3,000 )
Seat 2: ccc64 ( 3,000 )
Seat 3: Skraldeba ( 3,000 )
Seat 4: Slaven11 ( 3,000 )
Seat 5: papi21 ( 3,000 )
Seat 6: gustav ( 3,000 )
Seat 7: snowpaw ( 3,000 )
Seat 8: Masie ( 3,000 )
Seat 9: Houen7 ( 3,000 )
Tourney Level:1 Blinds(10/20-(no ante))
Houen7 posts small blind [10]
barry04 posts big blind [20]
** Dealing down cards **
Dealt to gustav [ 8s, 9s ]
ccc64 folds
Skraldeba folds
Slaven11 folds
papi21 calls [20]
gustav calls [20]
snowpaw calls [20]
Masie folds
Houen7 calls [10]
barry04 checks
** Dealing Flop ** [ Qs, Ks, 5s ]
Houen7 checks
barry04 checks
papi21 checks
gustav bets [75]
snowpaw calls [75]
Houen7 folds
barry04 folds
papi21 folds
** Dealing Turn ** [ 6h ]
gustav bets [187.50]
snowpaw calls [187.50]
** Dealing River ** [ 6c ]
gustav bets [468.75]
snowpaw goes all-in
snowpaw raises to [2,717.50]
gustav calls [2,248.75]
gustav goes all-in
** Showdown **
gustav shows [ 8s, 9s ] a Flush
snowpaw shows [ 5c, 5h ] full house, Fives full of Sixes
** Hand Conclusion **
snowpaw wins 6,060 from main pot with full house, Fives full of Sixes
************ Game 641612876 ends ************


any comments advice would be appreciated