I just sat down and have not done anything yet, so I didn't really want to "waste" KK by 3betting my second hand at the table.

Villain is unknown.

$0.50/$1 No Limit Holdem
5 Players
Hand Conversion Powered by weaktight.com

Stacks:
UTG ($81.90)
CO ($211.40)
BTN ($92.55)
Hero ($99)
BB ($120.70)

Pre-Flop: ($1.50, 5 players) Hero is SB
2 folds, BTN raises to $3, Hero calls $2.50, BB calls $2

Flop: ($9, 3 players)
Hero bets $7, BB folds, BTN raises to $17, Hero ?

What's my best line here?