Small claims is not worth it for $45, unless you are the type of person that cannot let something lie because of the principle of the matter.
You may end up getting your $45, but the headaches involved will probably not be worth it.
I'd probably leave it, and in the future not give clients files. You could maybe state in your future contracts that if agreement cannot be reached, half the retainer will be refunded or something like that. That way you aren't left with nothing for your time.