Pressed "i" button and lost 1/4 of screen

My screen was a little blurry, so after going through the menu options, I pressed the italic "i" button (to the left of the left arrow button) on my monitor. The screen turned black and said "adjusting..." in the middle, and when it resumed, the picture moved a quarter of the screen to the right, so the first 1/4 (on the left) is all black, and the right 1/4 of my screen is cut off. How do I undo this? I already went through the menu, but I can't get it to go back to using the whole monitor. Help!