Hi swm023,
The first thing that you need to do is to make sure that when you go to
the Existing Opportunities List screen, that the "Filter By View" dropdown
selection is Shared Opportunities.
If you are still unable to see all the records, you need to make sure
that you have permission to view other users records.
To check those permissions, you need to go to Customize > Users. Select your users' settings by selecting the Edit…. for your username.
Go to step 6 of 10. Verify your settings under the Sharing heading. In order to be able to see the other user’s
opportunities, you need to make sure that the dropdown selection is Full.
The reason that you probably didn't have access to any other records was
because your settings only allowed you to view the shared opportunities with
another user who didn't have any opportunities created.