If you delay paying, you must pay the Late Registration Fee. A class I wanted has no call number in the Class Schedule. Contact the department offering the class to obtain permission to enroll. You can register only for the number of units for which you have paid. Check to be sure that you paid enough.
Some classes have multiple parts such as lecture and lab or discussion sections.
These are corequisites. You must add each part of the class to your schedule separately. I made a mistake, or changed my mind after I hung up. Just call back and follow the instructions on the worksheet. Auditors pay the same fees as if enrolled in the class for credit, but the University does not count auditors in official enrollment.