8 week scan, small with irregular heartbeat

Today was our 8 week scan. The technician rescheduled for us to come back again next week. He stated that our baby is only measuring at about 6 weeks and has an irregular heartbeat below 100. Has this happened to anyone else before? Was everything ok? He told us to be prepared next week to be told it's an early miscarriage. I've had no bleeding but some cramping and one day of minor back pain.