How to come out

I know that if I were to confess to my parents that I was a lesbian, the reaction would likely not be That Bad. But I'm just afraid it would change the dynamic of my relationship with them forever. I'm 15 right now but I've never even had a girlfriend or even my first kiss. I've rejected plenty of guys and maybe I wouldn't be so romantically hopeless if I just gave it up and went out with them. I have the feeling that my mother wouldn't even BELIEVE me if I told her I was a lesbian unless I was like, dating someone. Not only that, but they'd probably be disappointed as well. She has specifically said things like "I'm so lucky my children aren't getting into the LGBT trend." Which pissed me off so deeply but I couldn't get angry at her without sounding too defensive.

In any case, I just can't come out by my own means even though I know I need to before they find out by some source that isn't me. What do