Random Res change {Cilent}

After champion select and the loading screen appears, I notice the screen is zoomed obviously realizing it was a change in res went to the options menu after I loaded into the match. I was able to change it back to my normal res (16.9) after I went into windowed mode. I just went back to full screen afterwards. I also asked if anyone else experienced this problem and I got a response of yes, telling him how to fix it.