[¯|_(ツ)_|¯]

While I don't own a penis/testicles, I have had doctor's appointments from the vagina side of things and get that they can make a person nervous.

I'd start out by writing down everything you want to discuss with her (for example, your voice, your sex drive, etc). Basically anything that you are questioning, write it down. I've noticed that I'll be in an office to discuss a problem and will forget a symptom or forget to bring up a topic, especially if I'm nervous or there's a lot to talk about.

I don't know if this is an option there but over here I'm always offered a chaperone when I have an exam of my genitals or breasts. It's customary in my gynecologist's (deals with the reproductive organs of those who were assigned female at birth) office, and there is also a sign at my primary care provider's office saying that if I want a chaperone at any point of the exam to please ask.

If you get an erection, you are NOT a bad person. Our bodies have a habit of responding to stimulus around us without it necessarily meaning that we are aroused or want to have sex with the person. Sometimes I react to my breasts being examined, but I'm asexual and definitely don't have any actual sexual feelings towards it haha. It's a lot less obvious for someone like me, but sometimes it can help to think distracting thoughts while you're getting the exam.