Due to the possibility of IUGR it is important for your dr to keep an eye on you. IUGR babies are at a significantly higher risk for intrauterine demise (aka dying) after 37 weeks. They can also stop growing and possibly lose weight if left in too long.
Yes PPs, growth USs can be off, but when we are talking very, very small babies it is really important to keep an eye on their growth. A lot can go wrong in a short amount of time.
I have been followed since week 28 for IUGR as has another poster on my BMB. My LO has been increasing in size and seems to be doing fine. If she wasn't we would be talking bed rest and early delivery. The other poster had hers early and she was a tiny thing who needed NICU time. The NICU time is usually needed for learning how to feed and needing to grow.
Don't stress, but do please take your dr seriously. Rest on your left side a lot! Eat more protein than you think possible, peanut butter, eggs, nuts, cheese. Ice cream has been suggested to help too. Babycenter has a great IUGR board. You don't have to join to read through the posts.