I looked up about the weight of babies, and I think it's all guesstimated and rough guesses due to measurements and how they feel...! I wouldn't get to hung up about it! Or worry about a bug baby. If there concerned they will send you for a growth scan.
My friend had a growth scan at 32weeks and were quite happy with the size, then at 36/37 weeks they were concerned and told my friend he was 3 weeks under his weight and size... So she was induced at 38weeks and had him, he was a healthy 7lbs 2oz... So just goes to show that sometimes they get it wrong!xx