Had my first appointment!

Went in for my first appointment today, based on my last period I should be 8w 2 days but baby only measured 6w 3 days. I did ovulate late, so I knew I wouldn’t be exactly at 8w. There was a beautiful heartbeat. 115bmp. But there is a blood clot behind baby. Anyone have experience with this? My doctor didn’t seem like it was a huge worry but I have a history of miscarriage. Just nervous. I go back in 2 weeks to make sure everything is still okay.