Scan measurements

I had a scan two weeks ago where only the gestational sac and yolk sac was visible, she said I was 5w5d. Today I had a scan and they are measuring me at 6w6 days, I saw baby’s heart beat which is a positive but I can’t help but worry that in the two weeks we’ve only gone up one week, I know nothing is accurate so early that’s why they don’t really rely on these measurements until the 12 week scan. Going by my dates of my period I would be about 8 weeks but I could just of ovulated later. Anyone else meaure a week behind and it be fine ?