League Streaming Problem

So, I'm kind of interested in streaming League from time to time. I have a microphone, camera, and a setup that can handle it.

However, I have trouble with OBS. When I tried to stream in the past, the game displayed in the upper left hand corner, only covering about half the screen. I would, of course, like it to cover the whole screen, so does anybody with knowledge on OBS know how to fix this issue?

I make YouTube videos, and when I record with Fraps it comes out just fine. It seems the problem is only with OBS.