Inadvertently locked into 2-column format landscape orientation

I was typing a default document and in the middle of a long, numbered, ordered list. The list started about the middle of the first page and continued onto the second page. Beginning on the second page, page orientation changed from portrait to landscape, and text flow changed to a two-column format. Additionally, any new file I try to open defaults to this format. Portrait format and one-column text on the first page, landscape orientation and two-column text on page 2. I may have inadvertently fat-fingered and hit some odd keystroke combination, but I don’t know. I can’t figure out how to undo this so the whole document is simply normal portrait and one-column format. Anyone have any suggestions? Or do I have to uninstall and reinstall thesoftware? Thanks!

First help us to understand what is at stake: OS name, exact LO version (as reported be Tools>About LO), save format. Attach a sample document 'at least 2 pages because something happens at end of first page).

At the bottom right of the windows there are three icons of pages, yours is set to Book view.
Click the first one with tooltip Single page view
BookView112348

Bookview was the issue! I must have fat-fingered or fat-clicked at some point. Thank you!