How to tell my parents I’m a fangirl

Hi so I’m 13 and I’ve LOVED one direction for about a year now (I always liked them but that was when I really joined the fandom) but no one really know I like them. Some of my friends know but they don’t really take it seriously. I want to be able to buy merch and posters and go to concerts but I can’t without telling my parents I like them. I also want to become more open with my mom in general and I think telling her would help (she’s pretty chill and I don’t think she would care I’m just nervous because being a fangirl isn’t really who she knows me as). How do I tell them???