Baby measuring small?!

So about 3 weeks ago I went in for my anatomy scan with baby boy. Everything seemed to be fine with him except the tech told me he was measuring small for how many weeks I was but all his body & organs looked great. So now I'll have to go back at 30 weeks & make sure he is growing up to standards. I'm very nervous, I'm starting to blame myself. Is there something I can do to make him grow better?  My doctor just kinda whatever the situation I fee & told me to wait till the next ultrasound. (Military hospital) anyone else's baby measuring small? I'm due March 1st