Hi Katmommy and welcome to BellyBelly.
I'm not too sure what advice to give, except that I have heard in a quite a few cases that the measuring they do of your bubs actually is not that accurate at times (eg. someone was told they were having a 9+lber, and he only ended up being 6lb!)
As for the weight gain, try to remember that every woman gains differently... How much is 47pounds? Is that about 20kg?
In my entire pg I put on almost 40kg... 8-[

Anyway, sorry I do not have any advice, but I just wanted to wish you all the best with the rest of your pg...