Measuring behind - only see sac

Erin

Based on my lmp I am 7 weeks and 4 days, went in for an ultrasound today and they said they are seeing what they expect to see at 6 weeks. They see a sac but too small to see anything else. I go back next week to make sure it’s growing. She didn’t seem alarmed but I’m worried since I know when I ovulated. Has this happened to anyone else and had a positive outcome?