First OBGYN appt.

Hayley
So I'm 17 and next Monday is my first OBGYN appointment. I had my mom set it up for me because I had my period nonstop for like 2 months. Anyway. So the OBGYN mailed us the paperwork to fill out and my mom was with me while I filled it out because I had to ask her about the past females in the family or whatever. And the "are you sexually active" question is on the same page and I had to check the no box. Well this weekend, I had sex with my boyfriend for the first time and I don't want her to know obviously. I also want to get on birth control which I think she was wanting me to already to regulate my period. But I want it to regulate my period and to prevent pregnancy. My question I guess is what should I do? Will my mom come into the room with me? And if not, how do I tell the doctor sorry I checked the no box, yes I am sexually active now? We've been together 2 years and have done oral stuff just hadn't actually had sex until this weekend. So if I tell the doctor I am, don't they have to do special tests? I understand that it's confidential (hopefully) but my mom and sisters work for my primary care doctor and I'm pretty sure at least one of them will see the information somehow if it's faxed. It wouldn't be the end of the world if my mom found out I was sexually active, just really awkward. What do I do?