My girlfriend (20F) won't stop calling me (19F) gay, what can I do?

Me and my girlfriend have been together for a year now and I love her more than anything in the world, but she seems to be very confused about my identity.

Now for context, towards the start of the relationship I tried to have a conversation with her because I didn't want her to be confused, in which I explained my situation. I consider myself to be a femcel, I don't believe any man will ever be good enough for me and therefore I don't ever see myself dating one. This does NOT mean that I am attracted to women. I aw not. The only reason we are dating is because I believe any women in better than any man and if I wish to date somebody I'll be happier with a woman even if I am not attracted to her.

Everything started out alright until she introduced me to one of her friends, it started out just fine with us getting along well, we had some small talk and drank lemonade together when out of nowhere, she makes a joke about me being gay.

Now I, of course, am happy to be the butt of a joke. I think that if a joke is told well enough it doesn't matter how offensive it is, but it just felt lazy and not that funny so I shot her a look and tried to make it clear that I wasn't happy with what she had just done. This only made things worse when they jokingly (both of them lesbians) started pointing at me and saying "haha! she's gaaaay!!!" which made me really uncomfortable.

Since then she hasn't stopped telling jokes about it around others or privately with me and I try to stress every time that I find it very weird and uncomfortable and I really wish she would stop.

I love her more than anyone, I care about her dearly and I don't want her to feel unloved by telling her I'm not a lesbian but this needs to stop. Does anyone have any advice?

TL:DR my girlfriend won't respect my identity and keeps calling me gay