Ultrasound measurements

So I have a history of ectopics so I have had an early scan done at 5w4d but was measuring at 5w1d. They said they could see heart movement but it was to tiny to actually detect bpm.

So a follow up was scheduled for 2 weeks. Yesterday I had the scan and I’m 7w4d but measuring 8w? Heartbeat strong at 161 but is it strange that I was behind 3 days first scan and ahead 3 days the next scan? I just want everything to be okay..and Any advice or input is greatly appropriate! Waiting for the doctor to call and let me know if I’m not longer high risk. Thanks 😊