it is normal for her to measurer any where from one to two week ahead or behind. Could be a larger baby or even a very short pelvis with an average or small baby. You cant tell the size of a baby by belly measurment. I wouldnt worry about it. But you are so close to holding your little one! How exciting!!!
I agree, nothing to worry about. I hit 40 cm. at 35.5 weeks. They gave me an u/s to check things out and it looks like I have an excess of amniotic fluid.