You will need to start over if you canceled before completion. If you do not wish to do a full backup, open OneCare, click Change Settings, then the backup tab.
Click Configure backup and Change Settings in the lower left.
Select your PC from the left side and uncheck "Turn on backup on this PC"
I recommend, however, that you not turn off backup, but evaluate what you wish to backup. The default file types can include many many files that you don't care about. On the page for "Your backup plan" - where the "Turn on..." check box is, click "Change this" in the "What" section. Select the file types you wish to backup - perhaps mail and pictures and documents. Note the amount of space each type takes up and remember that a CD holds 650 MB of data. Uncheck any types that you might not want to backup due to space considerations and the fact that they are not critical to you if lost.
At the bottom of the file type window is a "Exclude" link that you can further narrow down what is backed up by removing while drives, folders, or files from the backup plan.
-steve