I want to delete an apple ID I made at At&t store one day ago

So I bought an iphone X yesterday at the At&t store. Before I could leave, they said I had to make a call on the phone which required setting it up and making or signing in with an apple ID. Now, when I was little, my brother and I shared an ID and since I was the only one who bought things ($150-200 of music on itunes), and the fact that he doesn't use apple products anymore, he agreed to put the account in my name. At the store however, I did not have his account info so the At&t sales woman said I could just make one and change it later. Well here I am a day later and I find that apple won't let me change my shared-account-with-my-brother's email address to mine since now there's another apple ID using my email address. I tried creating a new email address and changing the shared account's email to it, but it refused. I also learned that you pretty much cannot delete an apple ID, but I need my music account connected to MY email address!! I haven't done ANYTHING with the new apple ID, so please please please just delete the one I made at the store. If I had known deleting it would be impossible, I would have made sure I didn't buy the iphone until I had the account's information!