Transitoning in high school?

[TroyTransistor]

I'm out to a few close family members, and I haven't asked them to call me Troy or male pronouns yet because I thought I could wait until college. I'm going to be junior in high school at the end of the month. I'm also out to my closest friends, who call me Troy and male pronouns, but none of them go to my school.
When I get home (I'm visiting my grandparents) I'm going to talk to my dad about transitioning because my social dysphoria is getting too intense. It's very damaging to my mental health. I know people are going to slip up with the name/pronouns because they've known me as something else for so long, but I can't live pretending to be a girl any longer. It will kill me.
The problem is, I don't know what to do about school. I'll email my teachers as soon as I find out who they are and inform them of my gender/name, but what about beyond that? Should I CC my principle on the message? How about my guidance counsellor? And what should I do about PE? I don't want to get changed in the girl's locker room, obviously, but I don't want to make the cisguys uncomfortable in the guy's locker room. Should I email my PE teacher and ask if I can just change in the bathroom?
I'm at a loss here, guys.
Thanks,
Troy

[wheat thins are delicious]

. Should I email my PE teacher and ask if I can just change in the bathroom?

Why ask?  I'd just do it. 

[Devyn]

Hey, Troy. We're pretty much in the same boat here. I'm going into 11th grade too.
A lot of people in my school know I'm trans, but none of my teachers know, as far as I'm aware.
I waited until I tried committing suicide to come out, so...I don't reccommend waiting if you know you can't wait.
I don't have gym anymore, but if I were you, I would email the principal or guidance counselor about it and see what they say. Why ask to change in the bathroom? Do it anyway. I always changed in the bathroom stalls in the girls' locker room.

You might want to know that coming out doesn't always go well. You most likely will get some harsh comments like I did when first coming out (I didn't come out to my teachers, though. Everybody just kind of found out, really. Once I started telling people I'm a guy, they had this sort of revelation, like, "WAIT, BUT I THOUGHT YOU WERE A GIRL." People get over it eventually though because most don't understand it.

Good luck. (: If you need someone to talk to, feel free to message me.

[Padma]

I'd say definitely start with your guidance counsellor, as they're the one who's most unambiguously there for your support. They should be able to help and advise you on how to go about letting the rest of the relevant staff know, and how best to ask for the support you want/need, like changing rooms.