We had our first ultrasound today. The baby measured 6 weeks 1 day, but the doctor thought it should've been at least 8…

We had our first ultrasound today. The baby measured 6 weeks 1 day, but the doctor thought it should've been at least 8 weeks. The baby also didn't have a heartbeat. We were told either I really am just 6 weeks, or I've miscarried and the baby stopped growing at 6 weeks. We're going back in a week to see if the baby has grown and has a heart beat. Has anyone else had something similar happen, whether everything turned out fine or not?