5w2d ultrasound. Just a sac. Thoughts?

Sarah

So I had an early ultrasound yesterday at 5w2d because I was having some cramping. All they were able to see was the gestational sac. Dr said it was normal, but he wants me to come back in two weeks to make sure there's a baby and a heartbeat. My hcg levels were already almost 8,000. Has anyone else experienced this and had a healthy baby?