It's awful when you're given worrying news and left to do nothing but worry! I think you should contact you ob or the MW's at the hospital and talk to them about the results of the US and the fact that you have been told your bub is not growing. The concern with a bub which is not gaining enough weight in utero is usually that the placenta is not providing bub with enough nutrients, but that is not always the case. FWIW, my DD1 was born at term and weighed 2.7kgs. The placenta was very healthy and so was she. She's now 8 and she is just a petite little person, she has just reached 20kgs.

Ring the hospital and discuss your concerns with them, see if you can bring your doctor's appointment forward.