Whenever you use your parents health insurance, they are sent a notice from the insurance telling them what the insurance paid and what they didn't pay. Additionally, a bill comes from the doctor's office for whatever the insurance didn't cover.
You need to tell your parents. Some insurance does not cover pre-natal appointments for children. This is one of the first steps in you being a parent. Getting the insurance situation figured out.
If you don't know if you are pregnant, take a home pregnancy test. Or you could go to a planned parenthood office near you - they do FREE pregnancy testing.
You still need to tell your parents as soon as possible.