NL50: KK oop, A hits river but flush draw misses

[Artsemis]

Full Tilt Poker - No Limit Hold'em Cash Game - $0.25/$0.50 Blinds - 8 Players - (LegoPoker Hand History Converter)

SB: $17.90
BB: $39.70
UTG: $6.30
UTG+1: $51.80
Hero (MP1): $75.45
MP2: $38.55
CO: $28.20
BTN: $49.25

Reads: <font color="blue">Villan is 35/13/2 over 100 hands. I checked the river planning to call a missed flush draw bluff -- though his bet was bigger than I expected. I have to follow through with the call, right?</font>

Preflop: Hero is dealt K[img]/images/graemlins/heart.gif[/img] K[img]/images/graemlins/diamond.gif[/img] (8 Players)
2 folds, <font color="red">Hero raises to $1.75</font>, MP2 folds, CO calls $1.75, 3 folds

Flop: ($4.25) 7[img]/images/graemlins/diamond.gif[/img] 4[img]/images/graemlins/club.gif[/img] T[img]/images/graemlins/club.gif[/img] (2 Players)
<font color="red">Hero bets $3.50</font>, CO calls $3.50

Turn: ($11.25) J[img]/images/graemlins/heart.gif[/img] (2 Players)
<font color="red">Hero bets $5.50</font>, CO calls $5.50

River: ($22.25) A[img]/images/graemlins/heart.gif[/img] (2 Players)
Hero checks, <font color="red">CO bets $15.00</font>, Hero ??