First ultrasound

Ju

Had my first ultrasound yesterday because I had heavy bleeding over the weekend. Found the heartbeat just going crazy in there. 🥰 She said it kept moving, can they move that early? I was 6w2d based on lmp. The sac was measuring 4w5d and the baby was measuring 5w5d. I honestly thought I would be a little farther along than that because I got my first positive at 9dpo. She said everything is how it’s supposed to be. Do measurements typically vary like that? Do you think it was maybe just the way she was measuring and might not be accurate? My husband said to stop worrying because it has a strong heartbeat, but it’s just kinda weird…