Baby measuring small

Tuesday I went to my 2nd visit and 2nd anatomy scan with my new ob doctor. After my doctor's visit was the ultrasound. It lasted about an hour or so. The sonographer said structurally everything looked great. Everything was as it should be except baby was measuring very small. She asked me if I had had an ultrasound with them before and I said yes, my last visit about a month ago. She asked if I has any previous ultrasounds I said my previous doctor scanned me and confirmed dates. She asked if I smoked tobacco or anything I confirmed I do not smoke, drink, and I even stopped my caffeine intake (minus the random chocolate deserts). Some history about me: I am a vegetarian, my husband and I aren't the largest people in the world me at 5'2 and him at 5'9. I asked her if they were going to change my due date. She said this far along unlikely but a doctor will contact me if the desire further testing. I haven't heard anything back yet and I've called a few times. This is my first child so I'm really nervous and not sure what to expect. Anyone told their baby was measuring small? What did they do? Should I be concerned?