Hi My Name Is Michelle, To Make This Short. Im

Hi my name is michelle, to make this short. Im 13 weeks and 4 days. so currently i had a ultra-sound and the nurse had said i was 15 weeks, 4 days ago. She had said the baby was measuring bigger then 13 weeks. im confused because i have not had sex so there is no way i can be 15 weeks. My last period was Sept 16, 2015 it was regular. i really need someone to answer this for me.