Starting testosterone and have to tell my parents

My parents have made it very clear that while they “support me”, they think that I shouldn’t transition physically at all, and that being trans/nonbinary is an internet phase. They excuse this with health risks (that are nowhere near as serious as they made them out to be), and personal experiences with friends who regretted transitioning. I know myself and who I am and what I want. And if I’m ever wrong I always have a backup plan, and it’s not the end of the world either way. They claim to be supportive but it certainly doesn’t feel like it. I made an appointment at planned parenthood next week to start testosterone, and now I have to tell my parents about it. I am an adult (19, 20 in 2 weeks) but I still live with my parents and they support me financially. They already know that I’m planning on starting T in the next couple months (and are firmly against it), but the elections in the US spurred me to act sooner. My therapist is in support of me, as are my friends, it just hurts that none of my immediate family is. I tell them in about 30 minutes, and just felt the need to put my anxieties out there, my friends know I’m telling my parents tonight and are super supportive, I guess I just want even more support? I think that’s fair, idk, just rambling at this point. Ty to anyone who comments :) I’ll probably be checking for them after I have The Conversation

Edit: I will be paying for the testosterone myself, although I will try to use my parents insurance since I’m still on it, if they refuse then I should be able to cover it myself. I included that they support me financially to explain the living situation a bit more, but I’ve saved up quite a bit and do have a job.