Measuring behind

Km • 27. Married 5 years. Our daughter Stella Claire is our entire world. Born Nov 15. 2015. Pregnant with #2 due in April.
I'm 32 weeks but measuring at 30. I've always been right on the week and I'm gaining weight. Doc isn't too concerned at this point but wants me to grow another centimeter or two by my 34 week appt.l or I need to get an ultrasound. anyone else measuring behind and everything was ok? It's freaking me out....:(