Regular condoms don’t fit me

I just had sex for the first time a few days ago, and it was fun, but during it the condom was slipping off. I assumed I just bought the wrong one, but when I went back to the store, every condom I found was 53mm in girth or bigger, mine is 45mm. I’m honestly embarrassed. But mostly scared, will I never be able to have safe sex because of this? Will girls laugh at me for it? I’m only 18, is there a chance it will get bigger? Is it possible there’s a medical reason?