Hi Sally,
There's no way to "undo" a course import, I'm afraid.
If your school allows it, instructors can "Reset" a course, which will clear all of the content:
https://community.canvaslms.com/docs/DOC-13069-415257102
This might work for you if you didn't have much else in the course besides the material that you just imported. However, it will also clear everything that was in the course before the import, so if you've already done a lot of work in the course, you'd have to redo everything.
Also, many schools, such as mine, do not show the "Course Reset" option to instructors, because of the potential for accidentally nuking the course in the middle of a term!
Mike
