Baby measuring 4 days small

I’m currently pregnant with baby #2. We had our 20 week scan today & the ultrasound tech told us that she is measuring 4 days small & in the 17th percentile. Im 20 weeks exactly today. I’m a bigger girl & when our son never measured small that we know of. Everything else on her u/s was perfect & I am feeling her move consistently. Has anyone else had this happen & go on to measure normally at future appointments? The dr was not concerned, but I am a worry wart.