PokerStars No-Limit Hold'em, $0.50 BB (5 handed) Hand History Converter Tool from FlopTurnRiver.com (Format: FlopTurnRiver)

BB ($90.45)
UTG ($13.10)
MP ($49.25)
Button ($54.60)
Hero ($49.25)

Preflop: Hero is SB with A, 5.
2 folds, Button raises to $1, Hero calls $0.75, 1 fold.

Flop: ($2.50) 9, 8, 8 (2 players)
Hero checks, Button bets $1, Hero calls $1.

Turn: ($4.50) 2 (2 players)
Hero checks, Button bets $1.5, Hero calls $1.50.

River: ($7.50) 3 (2 players)
Hero bets $5.5, Button raises to $11, Hero ???

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Villian is an unknown.

What's your play here?