Wemberly Worried by Kevin Henkes (2010)
Wemberly worried about spilling her juice, about shrinking in the bathtub, even about snakes in the radiator. She worried morning, noon, and night. "Worry, worry, worry," her family said. "Too much worry." And Wemberly worried about one thing most of all: her first day of school. But when she meets a fellow worrywart in her class, Wemberly realizes that school is too much fun to waste time worrying!