what he did wasn't legal but what you did wasn't either.
so, call the cops and tell them the merchant is holding your property. He may just file a complaint of the theft at that point. Then you may both find out what it's like to be in the defendants chair.
I suggest he may be holding the stuff so you will get your parents involved.
btw: whether you have the money now or had it with you at the time means nothing. You did attempt to steal. You cannot undo the crime.

