Genetic testing question

DH2015 • 💋💏❤️ married 3 years with a baby girl born Sept 2018 👶🏻🎀

Okay- I’m well aware that I am a bit anxious in general so maybe I’m crazy for even thinking this:

At my dating ultra sound they said I was 8 weeks, 2 days. They said the first day I can go get the genetic screening/gender blood test is at 10 weeks, 0 days which is March 6th.

In my crazy head I wonder if the test will be “more accurate” if I wait until like March 8th or 9th bc what if the dating ultra sound was off and I’m only like 9 weeks 5 days at the time of the test? Would this mean the test isn’t accurate? Should I give it a few days as a cushion? I really want the results as soon as possible, but I don’t want to doubt them when they come back.

The window to test is March 6- March 26. Does doing the test toward the end of the window make it any more accurate?

Thanks for any help at all.