I have 2 scans: 1st was done when the fetal age was 6w5d - scan says ga 7w3d. the 2nd was done when the fetal age was 9w6d- the scan says ga says 11w0d. which scan is likely to be the most accurate?

They're the same: The second scan is 3 weeks 1 day later, giving an age of 11 weeks 0 days. Adding 3 weeks 1 day to the 7 weeks 3 days means the first scan is giving an age of 10 weeks 4 days. The two scans have the same result... In real life, 11 weeks 0 days is the same as 10 weeks 4 days. They're the same. There is no difference. The numbers never tell the true age of the fetus, but are only estimates.

Earliest scan: The first scan is felt to be the most accurate done by a professional ultrasonographer as long as an embryo is seen not just measurement of a gestational sac.