There are two different measurements that can be used--Nuchal Translucency is used at 11-13w6d, and has an upper limit of 3mm. The Nuchal Fold is used after that, up to 22wks, and has an upper limit of 6mm. So, at your scan, it is still considered a useful tool for DS screening.
The nasal bone does look a bit smaller than I would expect on both of your images. IN the first image, babe has head tilted back a bit, so that can cause faulty measurements in the fold.
If I had done your scan, I would recommend followup screening at a Maternal Fetal Medicine Clinic as well. I have done that before, and totally normal babies have resulted. However, I would not being doing my job if I did not flag this stuff. There are a few that come back positive for DS.
At the next scan, they will do in depth measurement of the baby, and look at the heart in great detail. They will look for other "soft markers" for DS, and from there, you can make an informed decision whether or not to go ahead with an amnio etc.