hi, Thursday must seem like such a long time away when you have this chewing on your mind. I am no expert but I think the amino is the only way to diagnose it decisevly as it (Downs also known as trisomy 21) has an extra chomosome 21 present in the cells.
At this stage it is just a very small risk factor and your scans sound good. I would call him/her earlier to help you ease your mind.
I am sure everything is just fine. Good luck