NT testing

I did Progenity bloodtest and everything was fine. Results were negative. However, I went to do a NT screening at 12 weeks and received a nucheal fold measurement of 6.3mm, which is double the size they would want to see. This means I have a high chance now that our baby has Down syndrome or any other abnormalities. My husband and I are opting for an amniocentesis testing to confirm if our baby truly does have a birth defect or not. Has anyone been through this and got a false positive confirmed by amniocentesis or cvs texting? I am trying to figure out how common it is to have a false positive through NT screening. Appreciate everyone's thoughts.