Call or Fold on the river here?

[DonkeyDonk]

I think I played this fine, but I’d like to know if I could have taken another line.

I have a strong, aggressive image after winning several decent pots uncontested. Though it’s been early in the session, I’ve been in 50% of the hands, firing at will and nearly doubling my stack. UTG has been quiet, so no read on his play.

Online, $0.15/$0.30 NL Hold’em Cash Game, 6 Players

Hero (SB): $50.20
BB: $13.85
UTG: $5.45
MP: $63.05
CO: $108.50
BTN: $59.70

Pre-Flop: A[img]/images/graemlins/club.gif[/img] 7[img]/images/graemlins/diamond.gif[/img] dealt to Hero (SB)
UTG calls $0.30, 3 folds, Hero calls $0.15, BB checks

Flop: ($0.90) A[img]/images/graemlins/spade.gif[/img] 9[img]/images/graemlins/diamond.gif[/img] 4[img]/images/graemlins/heart.gif[/img] (3 Players)
Hero bets $0.60, BB calls $0.60, UTG folds

Turn: ($2.10) 9[img]/images/graemlins/heart.gif[/img] (2 Players)
Hero bets $1.30, BB calls $1.30

River: ($4.70) Q[img]/images/graemlins/diamond.gif[/img] (2 Players)
Hero bets $2, BB raises to $4

Now what? Obviously it's cheap to call, but it looks like I'm beat. I really thought it was a chop though. What does BB have, given the passive nature of his play until the river?