Scared Sick

So today was my first appointment with the fetal medicine doctor (not my first ob appt though). They did an ultrasound and told me baby has a 157 heart beat and was moving around alot and looked great. One problem though. On Aug 3, 10 days ago, I had to get an ultrasound done at the ER because I was having urinary retention. And on that date, they told me my baby measured 12 weeks 4 days. I was so excited because at that time, my baby was measuring 6 days ahead of where they were expected to be! Well, today I saw that the baby was still measuring 12 weeks 4 days. So it stopped growing and hasn't been growing for 10 days now is what that means, nevermind the heartbeat or movement. They should be measuring 13 weeks and 2 days by now. And even more scary, the nurse that took my blood told me point blank that if I test positive for trisomy 13 or 18 my baby will die for sure. And she didn't know what trisomy 11 was. I was so excited for my baby and now I am ready to burn all the gifts I got him or her because I know they will only exist in both an urn and in my heart. I am scared sick right now and very very upset.