First of all, EEs are a hybrid breed, and they can come in many sizes and lay different sizes and colors of eggs.
In my experience with new layers, most pullets start off very small, and get incrementally larger each egg they lay until, around a month later, they are laying the size egg they are genetically programmed to lay.
I like to save eggs from a new layer in their own special box, lined up according to the order in which they're laid. You are then able to see the very slight difference in size each time a new egg is laid. After three weeks or so, they are approaching full size.