I want to ask you how to solve this situation in the class.

In fact, this situation is quite common. There are always some activities that few people take part in, but the school requires everyone to take part in every class. At this time, the class Committee will be in a dilemma. Actually, that's how I used to be a class committee. You can make three chapters with your classmates. When there are not enough people attending the activity, you take turns in the order of student numbers, which is much fairer than random drawing. Besides, basically everyone will take turns.