I'm not sure why your high school is contacting your parents given the facts that you've outlined above - you are 19 years old.
Please consider the following information:
Under the federal Family Educational Rights and Privacy Act (FERPA), your became an "eligible student" when you turned 18 years old (as long as your parents did not obtain a legal guardianship over you, which I assume you would have mentioned in the facts, above). Assuming that your parents did not obtain a legal guardianship over you (court-process, so you would know), then the rights that your parents previously experienced regarding information and records access transferred to you at the age of majority - 18 years old.
Good luck. It can be difficult to self-advocate at times, but it's sound like you are well on your way to self-advocating!
Note: I am not licensed to practice law in your state and I cannot give legal advice to a non-client. I provide this response for general, information purposes only. This is not to be construed as legal advice. Consult appropriate legal counsel in your area.