Worried!

DG
Two weeks ago I went for an ultrasound (I'm 29 weeks) and my doc said my bbys head is measuring small :( but bbys weight is normal. On Wednesday I'm going to see a specialist for another ultrasound and I'm really nervous and scared! This is my first pregnancy....my doc said maybe the ultrasound tech just measured wrong but I can't help but feel worried. Has anyone gone thru this???