Mom Doesn’t Want Me On BC!!!

So I’m 16. My bf and I want to have sex but I refuse to until I’m on BC. My mom says things like I’m too young, I’m mentally not ready for sex, there’s no need for u to be on BC. She will not let me get it and idk what to do. I don’t wanna go on it behind her back cz she will more then likely find out and be pissed. How can I convince my mom to put me on it, idk how to tell her I want to start having sex. My mom says stuff like if I have sex there will be consequences like me getting pregnant which is the whole purpose of why I want to go on BC. Like omg would u rather have a grandkid? Please please give me some advice! (Id use just a condom but I’m scared it’ll break)