Measuring so far behind

Beck 👨‍👩‍👧‍👧🌈👶🏻🖤🖤🌈🤰🏻

Just wondering how common it is for bubs to be measuring so far behind I would be 10weeks today according to my period which where always spot on but dating scan I am 8weeks 5days I feel that's alot to be behind by.

Has anyones dates changed at the 12 week scan??