How can I get my boyfriend to use my preferred name?

I came out as trans (ftm) to my bf and he's supportive af, but he doesn't like the name I picked for myself because it's shared by one of my friends he doesn't like. I explained that before I met that friend when my hair was being awkward, I would refer to myself as Carter because I thought that I looked like a 3rd grader named Carter who would ask everyone if they wanted to play kickball at recess. He uses my pronouns and calls me a boy, but it's the name he doesn't like.