Accidentally registered to wrong phone

I bought a new iphone 4s. My first time connecting to my mac it asked if I wanted to register as a new phone or as another device, I accidentally selected the other device. Is there a way I can undo this and register as a new phone on my computer or will it always recognize it as the other device? Can I recover the lost contacts, pictures, & music? I have not messed with icloud at all.