Numbers: Gradebook

Numbers app:

When I open up a New Document for Grade Book, it already comes filled out for an example. It comes with five Assignment columns for you type in the grade for each student, when filled in you'll see the percentage equal amount change in the Total Column.

The issue I'm having is when I add another Assignment column to fill in a grade, percentage for Total column doesn't change. Does anyone know why?

Just want to note that I filled out the Due Date and Weight column exactly like the example.