I think you're misreading 'beat'. In the context of a drug deal, being 'beat' is getting less than you paid for. I'm pretty sure the kid was saying that if he didn't do the math properly, he'd be cheated on the transaction - I don't think it was a comment about corporal punishment.

Though I haven't seen the show, so I could be wrong.

ETA: simpleton, below, has cleared it up.