First display the diagram and show the page boundaries.

Using left click move the page boundaries so that the diagram starts in the top left corner of a page.

Now right click on the bottom right corner of the first page and holding the right button drag the bottom right corner down until the diagram fits on a single page.

This will also work to resize a big diagram for any sort of printing.
When printing to PDF files and wanting a single page, do not forget to select the largest page size supported. That way your pictures will be of the best quality.