Is it legal for my principal to make me take down my video that I took on the school bus?

From the wording in your question I will assume you are in high school. First Amendment Rights, such as free speech, can be limited in a school setting. In this instance if you video shows the faces of other students, and it was made on school property or on school time, such as on the school bus going to or coming from school or on a school sanctioned trip - field trip, going to a sporting event, etc. - then the school has the obligation to protect the identity of the other students in the video. Parents of students under 18 have the right to determine when or if their children are shown in a video related to their school experience. If you know all the students in the video you can obtain permission from them (if 18 or over) or from their parents to post the video. Present these permissions to the principal and request permission for you to post your video.

Can't tell on the facts. If you are in or this pertains to Michigan, you are welcome to call and retain Musilli Brennan Associates with details.