First GYNO visit 🙈

I am 17 and have extremely irregular periods. Some cycles will be three weeks long while others last only a few days. My mom finally made an appointment and got the forms for me to fill out, but because I am 17, she still has to sign for me. I filled out all of the forms and as I came to the last one, it asked me about my sexual history. My boyfriend and I have been dating for 6ish months and are sexually active. My parents do NOT know this and expect my siblings and I to wait until marriage. I marked “no” and “none” for most of the questions being asked on the form due to the fact that my mom/dad would have to sign the bottom of the form. Should I still tell my GYNO doctor that I am sexually active or will it affect my forms? Also, I am kind of nervous because I have never been...what should I expect?