Hi, not sure how much help I'm going to be but I thought I'd post anyway since I'm in a similar situation (ftm, starting university next year, also from a girl's school and also pre-hormones).
First of all, if you usually get gendered male that's pretty good for starters. More than can be said for me anyway haha (it's my own fault, I grew my hair 'cos I wanted to be a rock star and ended up looking like a woman). I assume you'll be using a male name and pronouns so that should give you an advantage in being perceived as male straight off. Also, remember that any new people won't know about whatever transition process you went through while at your current school, or remember you 'as a girl'.
As someone who has moved school a lot, I would say that most people are more interested in getting to know you and showing you around than prying into your previous school life. I don't know the details of your situation, but if the new school is far enough away from your old one there's a good chance the people you meet won't particularly know of it or that it is a girl's school. If you're not comfortable with that you could just try to avoid using the name, just refer to it as 'my old school' etc
At an early stage of transition you are unlikely to be able to stay in stealth mode long-term but you can come out gradually to specific people. If they get to know you as a guy first and then find out you're trans the 'dyke' label is less likely to stick. Remember that you are perfectly within your rights to not answer intrusive questions about your gender that you feel uncomfortable with. The basic stuff about pronouns etc should be fairly straightforward and anything else isn't really anyone's business.
As far as general anxieties go, it might help to get to know a few people from the school outside of a formal context first so you have a few familiar faces to help you out. Also, joining societies or getting involved with activities you're interested in can help you meet people and establish a friend group.
Hopefully this has been some use, feel free to private message me if you want talk about anything without putting it on the forum.
You're an awesome guy and if anyone doesn't see that it's only their loss so don't let it get you down!
Jay
