Fetus size & weight

I'm 36 weeks and had a scan at KK today. The measurements showed that my fetus is at 34 weeks+ and weigh 2.4kg+...Then doctor said if at Week 40 still haven't give birth then need to scan again...So I wondering is it normal for fetus to be 2 weeks behind and I also have not gained weight for the past 1 month but doctor said it's OK...#firsttimemom #pregnancy #Needadvice