Measuring behind, should I be worried?

Due to having a miscarriage before this pregnancy, I was having routine scans and checks with my early pregnancy unit. The last scan I had they measured the baby to be 7wks5days. I booked myself in for a private scan today which I should have been 9 weeks exactly according to the last scan I had. However baby only measured 8wks4days. I know it’s only a few days difference but should I be worried? The lady who did the scan said everything looked fine, baby moved 3 times whilst scanning and the heartbeat was fast and consistent. Therefore not to worry. However after last pregnancy, it’s hard not to. Please share your thoughts and advice x