I wouldnt worry too much about it. My friend's fundal height measured a 3 weeks ahead and she was told that her baby would be at least 4kg but her little girl was born last week only weighing 3.2kg. My friend did have alot of fluid throughout her pregnancy which the OB said is what made it difficult to judge the babies size.

I measure spot on but am not counting on that for accuracy at all.I just hope my bubs isnt too big