Periodically, I get my ereader stuck in some sort of screen zoom thing. I know I can usually escape it by hitting the back button or going to the home screen, but that tends to be a pain especially if it happens more than once while I am reading. Is this something I can turn off somehow? (I've looked through the settings, but I am not sure if I am just looking at this wrong.)
Unfortunately, it's impossible to disable the "zoom" function. Typically it's not something requested in user experience, and a disabling function would cause more harm than good.
What you can see are alternative options to avoid and get out of a zoomed screen, laid out in this guide.
While the back button is a way of reverting back to default, you can also pinch (by placing two fingers on the screen), moving inward or outward to either zoom in or back out of display.