I updated my iPhone and iPad Air to IOS 12 last night. This morning, my apps, like Instagram, are narrowed with black borders on each side. There is a double arrow sign present to expand or make the window smaller, but it no longer fills the screen. Any ide what happened, and how to fix it, please? I have searched all of my settings. If this were a desktop computer or laptop, I know about changing screen resolution, stretching, etc. What happened? Thank you