Hi,
    I have read your query & understood your concern
    * Nuchal translucency scan is a Usg scan done at 11 weeks to 13 weeks 6 days
       Of 
pregnancy. It is measurement of translucency  caused by fluid collection at the neck of fetus. This is a screening test for Dawn's syndrome in baby. It's   normal in your case means your baby does not have dawn's syndrome. 
    *Placenta is posterior & it's edge is touching the os. 
   -  Some times such position may turn to be a case of placenta previa( placenta over mouth of 
uterus )  which needs careful vigilance in pregnancy/delivery.  Such finding in early pregnancy demands carefulness.
   *   Please don't worry,  Many a times placenta shifts up in process of uterine enlargement & becomes safe.
   *  only thing you do is
   - take comparative/physical 
stress unless doctor  rest,avoid exertion till doctor declares the placenta to be in normal position.      
     -  Get regular pregnancy check up. follow doctor's advise strictly.Repete USG sacns as advised by your doctor, to know about placenta.
     - Take healthy diet ( proteins/vegetables/fruits/milk) & medicines as advised
     - Be positive.
  Thanks.