Measuring small

I had my 36 week doctor's appointment and my doctor said my tummy is measuring at 32 weeks. I haven't grown since my last appointment at 32 weeks. She did a non stress test and baby was very active. Now she's having me do an ultrasound on Tuesday to make sure he is growing okay and everything looks good. I'm so nervous and it's all I can think about. Did or is anyone else's tummy measuring small? Did it turn out okay? Did you stop growing before 40 weeks?