Is it legal to be forced to the gynecologist?

It can be legal if it is determined that there is a significant threat to the patient or to someone else and/ or that the person is not competent to make decisions for themselves (it's a general legal principle that minors are not competent to make decisions regarding their own medical care; their parents are expected to make these decisions for them... with a couple of significant exceptions). It is also legal to examine a minor over both the parent's and minors objections if there is a suspicion of abuse or some other serious medical condition. The details of exactly when these things apply varies from state to state and unless there is an immediate emergency usually requires going to court.

It is generally not legal to compel competant adults who present no imminent danger to themselves or others to any medical exam (and may still not be legal even if there is a danger to themselves).