Well, are you a minor or an adult? If you're an adult and your mother doesn't know, obviously there is more going on in that relationship and the medicos should really but out (but won't because people who don't come from dysfunctional families don't really understand about stuff like that). If you're a minor I could see some reason for caution.
I had a psychologist tell me she was really surprised I was ftm when I was pre everything and I had to explain to her that I pretty much wear men's clothing, live the way I want, get men's haircuts, and it's not really my fault my body looks like this on women's hormones. What sort of "drag" I am supposed to be in? This IS me. Then she realized how silly she was being.
The way your body look kind of conditions people how to respond to you. I'd tell the surgeon that "I live as me every day. I want my body to comport with me. The fact that it's not is causing me terrible dysphoria."