[Liz Smith]

I'm not exactly sure what your dilemma is, and I find your post a little confusing. My first response, with that in mind is that you need to get yourself organized. If you have an official game plan of what you're planning on doing, written down on paper, you'll probably get a more positive response. If you go in verbally saying "I want to do this", and sending informal emails around, its not as impressive as it could be. My advice is set up a formal meeting with your principal. If you have a teacher mentor who's committed to helping you, have them come to the meeting as well. If not, go around and ask them personally. It's easy to glance over an email and not respond, but if your there asking them in person so they can see your dedication and the great aspects of FIRST, it will be more likely that you'll grab their attention.
You probably shouldn't sneak around running things alone, especially if you've already been told that a teacher is required to oversee your actions. There are plenty of threads around which give advice on how to deal with school administration, and starting up programs like the one you have in mind. Search around the forums and I'm sure you'll find some more useful information. I applaud your motivation to do something like this and I wish you the best of luck.