If a Gestational Sac is seen on your USG, it cannot be an ectopic pregnancy. You should definitely go ahead and do a TransVaginal Ultrasound.

Ectopic pregnancy means presence of foetus in other parts of the uterus instead of in the cavity of the uterus. Presence of foetus means , foetus is always present with the gestational sac. It's very very rarely seen presence of gestational sac in one side and foetus in other side and try to consult any gynecologist and go to the clinical examination and repeat your ultrasound abdomen after 15 days and proceed further.

Show your usg and lmp details

It's very rare situation called heterotropic pregnancy But if the g sac in intrauterine 99% it's a intrauterine pregnancy