I understand this is hard to go through but please, calm down. EVEN IF your child is born with Downs it's NOT the end of your world. Downs is the easiest disability to work with. Most have some health issues but with medications and good medical care they live a lot longer than they used to, most live to be elderly old people now.
Some marry and even have normal children, some become actors, they work full time and earn a living. They graduate high school and can even, if their functioning is high enough, can attend college.
Downs is not a horrible thing. I've known many and worked with several married couples and even 2 that had children. Their children were perfectly normal. The genetic issue did not pass on to their kids.
I think you can accept that if it did happen it's going to be fine. It's possible the test is even wrong or messed up anyway.
Just please calm down, the stress is not good for you or your baby.