Anyone else scared of going on T?

I'm steadily approaching 18 and I always said I'd only think about going on T once it was an actual possibility, but now that I could actually realistically do it, I'm having doubts. I've been out as a trans guy for 4 years now but have never felt fully accepted though and a lot of people think I'm a girl. I've never felt comfortable standing up for my identity and making people refer to me as a guy either because I used to go to a really queerphobic school so I have left-over fears from that, even if my new school is really accepting. Because of this, I feel like I've never fully lived as a guy.

I've got two main fears: What if I'm not actually trans and I ruin myself for this and what if going on T makes me an ugly guy when I'm not that bad looking right now? I'm 100% certain I want top surgery in the future but for some reason T seems a lot more terrifying. I'm thinking maybe I should try be a girl again for a while to see if this is really what I want to do but the thought of that makes me kind of uncomfortable.