Kind of unsure about two things at the moment, first off, when I go to college in September, do I have to come out? 'Cause I know I'd be more comfortable going to college with everyone knowing I was male...but not trans* because I'd be scared then. But I can't really just say I'm male from the start, 'cause I had to go before for an interview type thing, and my mum was there, so the college staff think I'm female. And I don't even know if the staff are LGBT friendly or not, not to mention the other students. The second thing is just me debating whether to come out to my parents yet or not.
You don't have to come out unless you want to. I'm in a similar situation myself, except that I've been at my school for four years now, and everyone knows me as a female. Thankfully, there are a lot of LGBT friendly staff, including my choir director (who just got engaged to the man of his dreams). I'm also debating if I want to fully come out to my parents or just inform them of the name change - so they don't find out from someone else first. I don't have a whole lot of advice, other than that first sentence of mine. Also, you are not alone.
Like ThroughTheMist said, you don't have to come out. It's up to you when and how you do it, and if college isn't the best time, then that's fine. Most universities have a statement of their nondiscrimination policy, so you could look at that and see if it mentions gender identity. That's not a guarantee that they enforce the policy, but it's a good sign. You can also see if there's some sort of LGBT support center. Students are always a mixed group. Some you'll want to avoid, but some may prove to be very helpful. With your parents, there's a lot to think about: how accepting you think they'll be, how much you depend on them for support, and things like that. There isn't really a clear-cut answer, but you'll want to give it careful thought and preparation.
Thanks for the help people. I'll probably wait 'til I actually go to college, then have a good look around at the environment and the various policy. And I don't think I'm going to coming to anyone else yet.