20 week scan problems

Hi all. I have just come home from my 20 week scan. I have been anxious about this scan for a few weeks now. It started off ok with a heartbeat and lots of movement. She couldn't get all the measurements so sent us off for a walk to see if the baby would move around. I had already noticed that when she easured the femur that it showed up as 17 weeks instead of 20 weeks but she never mentioned it at the time.

We went back and carried on and she said she had all the measurements she needed. Then she told us that the stomach measurement brought down the overall 'score' (not the word she used but I can't think what it was)

She also said the femur measurement was very short and that the nasal bone only measured 3 mm when it should be measuring 5mm.

I have since talked to the midwife who said that she was also told that something showed up with the heart although we were told that the heart looked fine.

I am aware that it could be downs syndrome but at my 12 week screen I was told I was low risk so not to worry about extra screening.

Any thoughts?