misread my hand, winner mucks

[Spidar]

100+ rebuy tourny.

I thought this sucked, but but didn't know what to do.

I hold A3, raise from button and am called by SB. Heads up.

flop is 244. He checks, I bet.
turn is a J. he checks, I bet.
River is a 6. I bet. He calls.

I turn over my hand and say, "I have a straight."
He throws his cards in the muck where they are quickly shuffled in.
Table goes crazy. I'm stunned. I realize I misread my hand.
Of course a few don't believe me.

Though I think it's mostly his fault, I pull a $20 from my pocket and drop it on the floor. I then say to SB, "Hey, you dropped some money." He picks it up and says thanks.

Was I wrong?