First Ultrasound

Today I had my first ultrasound. According to my last period which was Nov 25 I’m suppose to be 7 weeks and 3 days.

The tech said she sees a sac but no baby. It’s not in my tubes and it was a very very small sac. So she said I’m most likely 4 weeks but I can’t help it but to cry and feel so scared. I’ve been trying for so long I can’t stop crying. I go in on feb 6th for another ultrasound. Has anyone had this happen before? The tech didn’t give me a picture bc the sac was so small