Credit card help

I have been on a mission to become debt free. My husband just came home with a $300 necklace for me (the chain on an old one broke a long time ago). He opened a Macy’s card to save the 20% and just paid it right off. I am very stressed now because I’m going to return It but I feel like they will only credit the Macy’s credit card and not actually give the cash back. How does this work? It was such a sweet gesture but I don’t buy myself things like that so I don’t want to keep It.