Cute, cute, cute!
The book suggests that when you piece the hexagons, you take care that the straight grain of the fabric is to the outside. This way, the hexagons won't stretch when you handle them as you arrange them. I think your comment about starch is right on. This will also help the fabric stay true. You might have stretched either the border fabric or the center a bit & got a few puckers.
I would not even have noticed it if you didn't point it out!