Weeks changing...

Anyone have any input in this. I had an ultrasound on April 8th and was measuring 7 weeks exactly. Today I would be 8 weeks 4 days. I was measuring 4 days behind based on lmp. Today I had another ultrasound due to spotting and thank God everything is ok. Baby is way bigger and with a strong HB. They said “your ultrasound shows that you are 9 weeks 1 day” which would put me one day behind based on lmp. I they didn’t tell me how many bpm the heart was but she did say it’s a nice strong heart. Has this happened to anyone?