When admission officials see your high school name on your applications, they are likely to recognize right away that it is a place where the majority of your peers will not seek higher education and where you have faced many disadvantages, such as the ones you cite here. So you don’t have to worry that you missed out on an opportunity to explain these drawbacks in your applications. Moreover, I assume that colleges will see from your applications that you are working hard to rise above your circumstances and that you are even helping other students to succeed.
Depending on the colleges on your list (and their admission-decision notification dates) it is not too late to send a supplemental “Additional Information” letter, if you act very fast. But I really don’t think that you need to do this. Admission officials make every effort to evaluate students in the context of their school and home environment, and they are usually able to understand what was available to each candidate in high school and what wasn’t.
If, however, in the weeks ahead, you learn that you have been waitlisted at any of your colleges, you can then write to admission officials to point out why their school would be a good match for you and also to “remind” them that the high school you attend does not provide the kind of support that many of their other applicants have had. If you emphasize your achievements in your letter, explaining that you “made lemonade from lemons,” the college folks will not view you as whiny, and it will help them to get a closer look at what you have overcome, although hopefully they will have realized it already.
Best wishes on good news this spring.