PokerStars No-Limit Hold'em, $2 BB (9 handed) Hand History Converter Tool from FlopTurnRiver.com (Format: FlopTurnRiver)

SB ($158.50)
Hero ($203)
UTG ($133.55)
UTG+1 ($216.30)
MP1 ($74.05)
MP2 ($317.75)
MP3 ($172.85)
CO ($191)
Button ($92.95)

Preflop: Hero is BB with A, K.
UTG raises to $4, 6 folds, SB calls $3, Hero raises to $12, UTG calls $8, SB calls $8.

Flop: ($36) 5, A, 8 (3 players)
SB checks, Hero bets $26, UTG raises to $121.55, SB folds, Hero ???

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This was my first orbit at the table, so no reads.

I know I should have raised more PF ($18-20 good?), but what's your move postflop?