If so, you have nothing to worry about, maybe the technician didn't know. Also, I had a very bad screening result for my first DE baby at a 1 in 7 chance of neural tube defect. As you are now, I was shocked and heartbroken. I managed to find a fetal specialist and went to see him. He told me that there were many things that swayed the results: one was IVF, another was fetal demise (I started with triplets), another was either parent being of African decent, another age of egg.
I don't know if any of the above things relate to you. Did they use your age in the calculation of the blood work as downs syndrome results are swayed with age. Also was your HCG high - my eldest daughter always flags for downs as her HCG is always high and she donated for a lady on the board and the first thing I noticed about her pregnancy was her extremely high HCG. So many things come into play but as you mentioned that the embryos were tested before, if that's the case I wouldn't worry in the slightest.
Big hugs, I know it is such a blow to get news like this in the midst of all the happiness but normally its no problem.