Still worried

I am 32 years old and expecting our second child. With 16 weeks I had a blood test done wich came back 1:450 change for Down syndrome wich is close to the cut off for Down syndrome. With 20 weeks i had a ultrasound done and they saw one soft marker for Down syndrome wich is an echogenic focus on the heart. The hospital phoned me and offered if we wanted to do an nipt blood test or amniocentesis. Our risk came down to having a baby with NO Down syndrome at 99.4 percent. Anyone experiencing the same or had ? What shall I do The nipt or amniocentesis? I know the results are pretty good! But l keep thinking about it