100NL: Kings on low paired board

[Aero1441]

SB: $120.45
BB: $60.00
Hero (UTG): $311.70
CO: $93.65
BTN: $129.55

Pre-Flop: K [img]/images/graemlins/spade.gif[/img] K [img]/images/graemlins/heart.gif[/img] dealt to Hero (UTG)
Hero raises to $3.50, CO folds, BTN calls, SB folds, BB folds

Flop: ($8.50) 7 [img]/images/graemlins/spade.gif[/img] J [img]/images/graemlins/club.gif[/img] 7 [img]/images/graemlins/club.gif[/img] (2 Players)
Hero bets $6.00, BTN calls $6.00

Turn: ($20.50) 8 [img]/images/graemlins/spade.gif[/img] (2 Players)
Hero bets $18.00, BTN calls $18.00

River: ($56.50) 3 [img]/images/graemlins/club.gif[/img] (2 Players)
Hero checks, BTN bets $28.25, Hero ?

Can you guys please check if my lines are correct? And what do you recommend on the river? Do I beat anything here? Can I actually fold for this cheap? Thx for any advice [img]/images/graemlins/smile.gif[/img]