Girls, I had an ultrasound - they said the fertilized egg is formed ac…

Girls, I had an ultrasound - they said the fertilized egg is formed according to schedule, but the embryo is still small, like it's a shorter term. Is this normal? I wanted to hear the heart - the sonographer says that even if it's already 7 weeks pregnant, the heart isn't heard yet. They scheduled another ultrasound for Friday. I'm so worried about it.