What should i expect at a checkup for a 16 year old girl? do my parents have to be in the room? if not, what will they tell my parents? and can i refuse parts of the exam im uncomfortable with?

Parents have access tp the medical record of their children who are minors. In some jurisdictions, the law permits minors who are not emancipated to receive confidential services relating to contraception or pregnancy testing. Here is a helpful site with more info https://www.ama-assn.org/delivering-care/ethics/confidential-health-care-minors

Every Pediatrician handles adolescent visits differently. In my practice I see all adolescents 14-15 years old and up alone (with a nurse in the room for any breast or genital exams), and 12-13 year olds with their parents for part of the visit and alone for part of the visit to give them privacy to ask questions and I can talk about drugs, alcohol, sexual activity or other private matters.