@LauraDiPietro1 That should not be possible at all. Are you totally positive you are editing the copy and not the original? If the enrollments really did copy over, you need to reach out to Canvas support immediately, as this forum is just other educators offering answers and none of us have the access to resolve anything in your instance.

If you were to go about this yourself, you need to remove the users from the People page. You should be doubly sure this is the right course shell before removing any students from there. If you go this route, grades will be removed when the students are removed.