iBooks display on my iPad

On my ipad, iBooks, I have been using this for reading books for years. Last week, I was reading horizontal (it shows the full page), my cat stepped on the screen and all of sudden it shows 2 pages in horizontal instead of 1. Can someone please tell me how to change it back. I asked the cat, but he's not saying a word on the subject. I've tried to change it under settings, but to no avail. Thanks