Ultrasound Results

Based on my last menstrual period, I’m supposedly 7 weeks and 6 days today. But based on the results of my first ultrasound yesterday, my embryo is just at 5 weeks and 6 days (probably, and hopefully, 6 weeks today). I’m a little worried that my baby is growing a little slow? Somebody here had the same case and their babies developed just fine in your mummy tummies?