Maternit21 test

ATM

I'm 14 wks 2 days today & had the test at 12 weeks. Results came back negative for chromosome abnormalities and says gender is a girl. My thing is the fetal fraction was only 4%. I've read where average is 10. Nurse said it was fine, but it just seems low to me. It wasn't flagged for low though. Could my results be inaccurate bc FF was only 4%?? Anyone else have 4% and everything be fine? Tks!