Telling my mom about...his dick?

Meagan
My mom and I recently agreed to get me on birth control before may 2017. I'm now 17 years old and I have a boyfriend who I love and cherish more than anything. He's 7 and a half inches, no lie. I've seen it before. Because of this I'm scared and really don't want a IUD. I want the implant. Any suggestions of how I should tell my mom this? She will definitely ask.