I had a lot of similar worries before presenting fem myself. Hell, even your high school experience feels similar to mine. I will say though, that I've gone full fem everywhere in my life, and it's one of the best feelings in the world. Granted, I have passing privilege, and I worked on my voice a ton before presenting fem in public, so YMMV, but I'll tell you how I deal with some of the stuff you have worries about.

As long as I put makeup on, I have passing privilege. But if I go out without any, my lip shadow (from facial hair) is quite noticeable. I've had people take notice of it, but I have enough feminine cues that people generally treat me as a woman regardless. The voice helps a lot, I must say. It's hard, it will take a lot of work, and likely help from a professional to get exactly where you want to be, but it's worth it in my experience. When I was at work prior to presenting fem, and someone perceived me as a woman, I used my "old" voice, and they immediately said "oh, sorry dude" or similar. I think the biggest thing that helped quell my anxiety was just going full fem, and realizing that even without the makeup, no one really cared. I just presented fem enough to be gendered correctly, and regardless of whether or not people knew I was trans, I was generally just treated as a woman. It also helped for me to understand (through therapy) that other peoples' opinions of me don't make me any more or less valid. I'm a woman, and no one's opinion is going to change that fact for me.

As for transphobia, I'd deal with it the same way I deal with misogyny. If it's someone I don't know, I'd just put a smile on and pretend like nothing happened, while doing whatever is necessary to get out of the situation without provocation. My experience is that fighting back is just gonna provoke the other person, and they don't get the same sense of power if you don't show them the reaction they expect. The situation is more complicated with friends and coworkers. Honestly, I've been lucky enough to not deal with transphobic from friends or coworkers, so I don't have any experience there to give guidance. I will say though, you shouldn't let that experience dissuade you from being true to who you are. No one should have to hide themselves because of someone else's perception of who they should be.

As for the feeling like you're intruding part, I can say that I no longer get that feeling for being trans. I feel like I belong in the women's spaces I'm in, and I no longer have the constant anxiety of thinking I won't fit in. The fact of the matter is that I'm generally welcomed with open arms, and I'm able to engage with other women in ways that didn't feel possible pre-transition.

It's easy to get caught up in thoughts about how other people will perceive you, but the best advice that I can give is that you should live your life a the way that is true to yourself. You shouldn't be forced into presenting as someone you aren't, or feel pressured by other peoples' beliefs of who you should be. Granted, that's easier said than done, but I've spent a long time at this point learning that, and allowing myself to live as my true self has been perhaps the greatest decision of my life. I could never go back at this point.

yeh i had the same feelings when i was 13. always being off in the eyes of society, not in my own eyes though. also a thing that consistently bothered me was that i couldn't just hang out with the girls ... like why not? why is the world so pointlessly wrong about this? i'm sure i would have been good company. anyways, it was probably something about "we have to keep the girls safe, so the boys can't come to visit them" or sth ... the rural environment i grew up in was very christian in that way. i hated it, needless to say.

the way i handled the only blatant tranphobia i have experienced was when me and my fiancee (both queer) were at a restaurant and this creepy old dude right next to us was openly glaring at us without taking his eyes off us. after abt 5 minutes i got sick of it so i stared into his eyes until he got uncomfortable, then he left shortly after without another glance. it was actually pretty empowering. most of these dickweeds are little insecure pussies deep down. :)

I think I have a very similar experience, I've had social anxiety for as long as I can remember, prior to that I think I was just very quiet, I'm not sure if I have autism though, I just know I developed a social anxiety disorder gradually.

It also makes so much more sense to me now that I know I have gender dysphoria, in the past few years a lot of the social anxiety had shifted toward gender fueled anxiety, like I'm being viewed as someone inherently less safe to be around, or that I'm intruding. It probably didn't help I went to a boys secondary school (when I developed the social anxiety and dysphoria), and then in sixth form was thrown into classes with almost all women, I'm sure if I were placed back there I would feel just as bad as I did when I was taking classes there. I've since gone and changed my name legally so I've basically killed off my ability to boymode now (mostly).

I think you should go as yourself, but it's all up to how you think you'd manage. I know myself that nothing bad will happen, the worst case is I'll just run home and not even attend. For me I'm trying a strategy of just taking myself somewhere, like to an event, and then worrying about it, but sometimes that doesn't work out and I should've probably prepared myself mentally instead.

I hope all the best for you though, try to take it easy, I know it's hard <3