9 weeks only gestational sac and no baby seen yet.

I had experience this before. Supposedly 9w according to implantation, but when i come for scan, they found nothing! As if i’m not pregnant at all, so they ask me do hcg blood test & must repeat in 2 days if the results doubled means pregnant, if decreased means miscarriage & if go up slowly not even doubled means ectopic! 2days later it turns out doubled, but still cannot see anything but a yolk dot smaller thn 5cents coins, they concluded it’s early pregnancy so instead of 9w i was only 5w, it happened when we ovulating late or something! Why not ask for blood hcg test?