I think you can change your school record. Your guidance counselor should know how to do that.
Do you already have a College Board account? If you identify as Hispanic why didn’t you choose that? You’ll have to contact them to ask how to change their records. If you don’t have an account you don’t have to change records. Just pick what ethnicity you want.
The next US Census is in 2020. You’ll be able to identify however you want then. But you can’t change past census records.
None of this will help you with college admissions if your heritage isn’t reflected in your app. What, exactly, are you planning to explain to admissions officers?