Possible Downs at 21 weeks

I am 35 years old with two beautiful, smart and active little boys, ages 8 and 5. My husband and I decided to go a third and last time to try for a girl. We did it! It's a girl! That day was one of the happiest days of my life. The doctor offer us the genetic screening test because of my age however there is nothing on the ultrasound to indicate any problems. The screening came back positive for trisomy 21 (downs). The screening is not 100%. So they offered an amino which is 100% but we declined because we will love our baby no matter what! But now I am stressed! I can't stop thinking about the future, her future! I don't know what to expect! I'm nervous, anxious, and sad all the time! I have plenty of support and a number of women who have gone through the same thing and their babies were born without downs. That gives me hope but not much. If you have gone through this I would love to hear about your experience! Maybe it will give me some comfort. Thanks!