Ult went from 6w5d to 8w3d in three days?

I had two ultrasounds this week as I’ve been passing blood. Both showed a healthy heartbeat. The first was a vaginal ultrasound and said that I wasn’t as far along and only 6W5D, when I should have been 8w. Then three days later the bleeding progressed and I passed clots. They did an abdominal ultrasound and the baby measurement showed 8W3D. The pictures look significantly different as well. The first was a little dot (fetal pole with heartbeat) in the black sac and the second was what I was expecting- oblong baby with a heartbeat fluttering in the middle. Is one less accurate than the other?I know they have growth spurts but this is more than I was expecting in 3 days time (Mon-Thurs). Same tech, same machine, only difference was vaginal vs abdominal.