get (one) wrong
To misunderstand one. Don't get me wrong, I appreciate everything your mother has done for us—but it's time for her to get her own place. You've got him all wrong—I know he seems gruff, but he's a total sweetheart.
get (something) wrong
To do, understand, or answer something inaccurately and/or incorrectly. I sure didn't ace the exam, but I hope I didn't get too many wrong. Take your time—you'll just end up making more work for yourself if you get it wrong the first time. That electrician got the wiring wrong, and now nothing in the house will turn on!