I wpuld ask if they would do another scan. There is a big difference between 5 and 8 week scans. Did they say everything was ok? Did they offer you to come back because of the big difference in your calculations?
Hey, I had something similar, we thought was 12 weeks and scan suggested was only 9. Baby developed just fine and is now 6 weeks old
I went die a scan thinking I was 8 weeks but was only 6. They said its just because my cycle must have been longer when I conceved xx
I had a reassurance scan at 9 weeks and he measured small and so they said I was 6 something weeks even though I knew exact date of period and when I ovulated. He was only 1 day behind by the time I went to 12 week scan! I was told in first scan there is usually a 2 week discrepancy plus or minus so early on as baby is so small.
I didn’t have as big of a gap but I thought I was 6+3 and was 6 exact they said it’s normal but I don’t know how much time either way, could be you ovulated late? Can you call back have a second opinion?