Villain in this hand is on BTN with a full stack and is 43/13/.6 after like 30 hands. I am UTG with a full stack. It's pretty obvious that I have an overpair on the flop. It seems hard to give villain credit for bluffing the A on the turn thinking I can't call. I have to fold even with 1/2 my stack in there right? What can I be ahead of?

$25nl 9 players

Hero raises to $1 with
UTG+1 calls $1
UTG+2 calls $1
BTN calls $1
SB calls $0.90

Flop: (Pot = $5.25)
SB checks, Hero bets $4, 2 folds, BTN calls $4, SB folds

Turn: (Pot = $13.25)
Hero bets $8, BTN raises to $20 and is all-in, Hero ???