Baby small for 10 weeks

t+s

I went for an ultrasound at 10 weeks 1 day and the technician said the size and heart beat were right on track and it was moving around a bit. Then 3 days later my doc's office called and said they were a bit concerned that the baby is small and asked me to do another ultrasound a week later. Should I be worried at 10 weeks that the baby is small? I've had 2 miscarriages in the past and everything seems to get me worried!