Can someone help me interpret what my obst told me at yesterday's ultrasound?

I thought I was having an NT test. I'm sure that's what he told me a month ago. But the doctor didn't seem to measure the back of the neck. It seemed he measured the distance between two bright lines either side of the lower spine. He told me the distance was 1.6 and I should only worry about Downs Syndrome if the distance was greater than 3.

Yesterday I was thrilled to hear him say everything was fine, now I'm wondering if he did an NT test or something else. I got a printed report that said no abnormalities detected. And he said I will have more blood tests in a month. But I read that the blood test and the NT scan should only be a week apart.

Does anyone know enough technical details to put my mind at rest? (Flipping hormones - yesterday I was so happy and relieved, today I'm so worried.)

I'm in Vietnam, the obs is French and this is my first pregnancy so I'm really not sure what's going on.