Hello Shannon,
Thanks for writing in! Please note that only pages created in Cornerstone will be displayed on the sidebar. Any pages created outside of the Cornerstone builder will not display. You will have to go to Pages > All Pages and select which page you want to edit in Cornerstone.
Remember that when a page is edited in Cornerstone builder, those contents that were made outside of the builder will be discarded and overwritten.
Best Regards.