Mom bought be $300 necklace but I don’t want it

How do you politely tell your parent you don’t want their gift. My mom bought me this necklace with a cross on it. And wearing crosses ain’t my thing. She told me “ you need it god will protect you”. But I don’t believe in that. I told her I wanted a necklace with my name on it but she went to buy this instead for $350😶 like $300 on a necklace... I could have got the name necklace for cheaper. I don’t want to sound rude or ungrateful but I’ve been talking about wanting a name necklace for months even my sister knows, so why would she buy this. How do I politely say she can take the gift back without sounding ungrateful.