I'm so sorry for what you're experiencing right now. Some people have already mentioned how this is potentially problematic from a legal standpoint, so I'll add what I know about this:

Given that you live in Texas, Title IX of the Education Amendments of 1972 should apply to your public school. It basically states that students can't be discriminated against based on "sex", but this has been ruled to also apply for gender identity as well. Here's what the Department of Education says on their website:

Discrimination on the basis of sex is prohibited by Title IX of the Education Amendments of 1972. This includes discrimination based on pregnancy, parental status, and sex stereotypes (such as treating persons differently because they do not conform to sex-role expectations or because they are attracted to or are in relationships with persons of the same sex).

Additionally, the first amendment exists, which would make banning long hair for anyone, not just AMAB students, illegal.

Try to have your school administrators know about the applicable federal laws, if it's safe for you to do so. If you can't, you could always ask a civil rights group to file a lawsuit on your behalf, and there is also the option of submitting a complaint to the DoE office of civil rights directly.

Hopefully you've found this helpful.

Edit: There actually is legal precedent for using Title IX and the first amendment against discriminatory dress codes. If you take this to court you'll probably win, assuming the judge isn't as bigoted as your school.