Your report design is not saved until you click the Save button on the Layout Tab. If you design complex criteria and calculations, go to the Layout Tab regularly to save your work.
CAUTION: Before you copy a report, review the other topics in this document and study the behavior of Report Writer features. It isn't necessary to use the options on every Tab of the Report Writer window, but an understanding of how each works is essential to create a report. The Layout section is especially important.