measuring a week behind

Jessica
I'm on my weekly appointments now. 36 1/2 weeks. Baby heart beat was good, movement not an issue. My doctor was just concerned about the size the baby is at. It's the same from last week. So i scheduled an ultrasound for Friday. I'm not going to lie that I'm not nervous. Actually cried when I got in the car. I'm hoping it's nothing serious. 
If the baby is in the 10th percentile I'll have to be induced. If it's in the 15th-20th I'll continue on my own. 
Has this happened to anyone? Can someone please ease my mind?!?