You may or may not get a demand letter from Shopko. Shopko may be entitled to recover from you the costs of recapturing assets, restocking, etc.; however, the cost shouldn't be that much, and the fact that you are underage may prevent them from doing so.
In accordance with the Avvo community guidelines, this communication does not constitute "legal advice", nor does it form an attorney-client relationship. You should seek counsel in your geographic area regarding any specific questions.