It is halachically permissible for an unmarried woman to have a Pap smear or a gynecological examination for any purpose. Halacha strongly encourages taking care of one’s health, and if a physician recommends a Pap smear a woman should not hesitate to do it because she is single.
The vaginal opening is partially covered with the hymenal tissue that is formed as part of development of the female reproductive system. The size and shape of the opening can vary from woman to woman. Under normal circumstances there is an opening large enough for menstrual blood to exit, and for tampons to be inserted. A gynecological examination may stretch the hymen somewhat, but that is halachically acceptable. Often, the hymen has been stretched already by physical activity.
From a halachic standpint, being a virgin means not having had sexual relations. It is not related to the status of the hymen.