Stomach measuring behind?

So i went to the Dr Tuesday I'm 2cm dilated 75% thinned. But when he measured my stomach he said I was measuring2 weeks behind. He said that its not a concern until it measures 3 weeks + or - .... has anyone experienced this? This didn't happen with my first. He Said if I have not grown by next apt on Tuesday that they will do an ultrasound ti make sure she is growing properly, and also my fluid isn't leaking. Just curious if anyone has experienced this and what happens if on Tuesday I havnt grown , will they have to induce ? Thank yall!