Optional days

Just a quick question. I am doing FB Strong right now and it has a sixth optional workout every week. I am going to skip those, since I am already stretching out the program and doing 2 or 3 workouts a week, so I’d rather do the more intense workouts on those days. But I was wondering if I need to mark them as completed to have the calender think I completed the program? It sort of feels like cheating to mark them complete, even though they are optional ;-).