As of now u need not worry about a single assessment of OFC if ur baby is gonna have normal developmental milestones. Ur doctor will track it in subsequent visits and will tell u if there is a significant problem in future assessments. Again there can be inter and intra observer variations as well.
Next Steps
Track your babies developmental milestones and report if there is a significant delay.
Health Tips
There can be variations in assessment, so need not panic about these numbers unless your doctor feels there is something significant.