[Django]-Page not found (404) Error on Django:

Actually, you are getting 404 error from here.

 step = get_object_or_404(Step, course_id=course_pk, pk=step_pk)

Here (get_object_or_404) you are saying that if unable to find a Step with given course_id and step_pk then give 404 error and it is doing the same.

You need to make sure that the entries exist.
Your codes seem fine.