" You will have to go to the head master." Okay?

“你得去找校长。”好的？

So if you're late, you have to go to the head master.

所以如果你迟到了，你必须去找校长。

In school, the " principal" is the director or head master or leader of the school.

在学校，“校长”是学校的主任或校长或领导。