As an aspie I definitely understand the desire to go for the more specialized route. I study paleontology, which is a small, interdisciplinary field; a pretty even mix of biology and geology. My solution was to double major, because there really aren't any programs with a paleo major.
In your case, if you can't go to one of the schools with the screenwriting specialty, don't worry, you will be fine with one of the other schools. You may not like the gen eds as much, but they will be good for you. Even if you are going into a specialized field, it is helpful to have a broad base of experience. It looks good to prospective employers, and it gives you more to fall back on when you are just starting out and trying to get a foot in the door. A lot of times that foot in the door may need to be in a bit of a round-about way; taking a position that is near what you want, but not exactly it. Sometimes you will need a completely unrelated job to support yourself until something better works out.
You can also supplement your classwork by doing your writing on the side and working to get that writing out in some form. Since it is not my field, I don't know entirely what is out there, but student groups are always an option. I know one of my friends in undergrad did a production of a script she had written with friends recruited as actors, although I know doing something like that would probably be difficult for an aspie.
I'm working on my masters now, and in the last few years I have learned that the way to be specialized is to have a variety of classes and experiences, many of them generalized, that all revolve around your final goal. Class A, B, and C may all be fairly general, but if A, B, and C are all pertinent to your field, then it can often be better to take the three rather than taking one single class that synthesizes A, B, and C.
As for things like math, science, etc., do your preferred schools not require them? Can you test out?
Just, don't limit yourself by thinking that there is only one path toward achieving the career you want.