why is the viewing area of my samsung android tablet smaller?

[AC Question]

I'm reading books from my city county library through Overdrive. The screen for the text has gotten smaller. I cant see whole pages. I've tried zoom, pinching and full screen mode, as wellas Overdrive help, which discusses library access etc. Overdrive doesn't. Address technical issues. So thats no help. None of the above has solved my problem.
What should I do?