Ultrasound question! Nervous FTM

I had an ultrasound at 7 weeks, and the baby was measuring 7 weeks 4 days. This week, I had an elective ultrasound done at a separate ultrasound place (not my regular doctor) at 10 weeks 1 day. Because of the measurements of the first ultrasound, I expected baby to measure 10 weeks 5 days, but it measured 10 weeks 1 day (so four days behind if I'm going by size of the first ultrasound). The baby was moving all around and has a strong heartbeat of 170, but should I be worried about the size based on the first ultrasound? I'm going to mention it to my midwife at my appt this week but I'm just looking for any experiences with this.