The Report Cards will generate even if the Review process has not been completed. In order to stop Report Cards from being accessed if the review process was not completed, you would need to remove the Report Card viewing Access Dates for constituents. This will allow you to finish the review process without users being able to see "un-reviewed" grades. You would then need to go in and enable constituents access to Report Cards again. To change this go to:

onRecord > Performance > Grading 

  1. Report Card Builder
  2. Select the report card to edit
  3. Click Access/Grades
  4. Click Edit Access/Grades
  5. Enter the revised Dates