Dear Ms. Smith,
The developmental charts offer a roadmap or guideposts to development. They represent an average or norm, and many children do not conform to them in a precise manner. Rather, what most children demonstrate is conformity to the 'charts' in some areas of development and variance from the charts in other areas. In other words, development is not a steady, even progression in all areas. From the information you provided, there's no reason to be worried.
Thanks so much for the encouragement! I'll try not to worry so much!