Don't have any first hand experience with this, but have heard numerous stories of moms who had negative screenings with perfectly healthy babies. Have also heard that the amnio is much more accurate than the screening, what does your OB/GYN say? I kind of wish they never did those tests, to a doctor it is a number on a paper, to you this is your baby!
Can tell you that I was on a prescription medication that you are not supposed to take while pregnant when, surprise, found out I was pregnant. I spent 7 1/2 months worrying myself crazy that I somehow damaged my baby without knowing it. My son is now two and extremely healthy in every way. If you can try to not worry, just enjoy the new life growing inside of you. When you hear that cry for the first time, your beautiful baby will win your heart no matter what happens!