Pages organized backwards (inner margin on the outside)

[Greatship485]

Greetings. I'm new to this forum. I have a problem. I use OpenOffice to format books for publishing. So far it's been great, but in the file for my latest book I notice that the pages are suddenly displaying backwards when I zoom out to view the file as mirrored pages. They seem fine and right at 100%, but when viewed smaller so that the pages show side by side the inner margin of the page is on the outside. Is this only a display issue or is there something wrong with the file?
Running OpenOffice 4.1.7 on Mac OS 10.14.6

[Bill]

There are three icons in the Status Bar. The first is Single column, the second is Side by side and the third is Book mode. Click the Book mode icon, not the Side by side icon.