In-Game League client stuck on small screen in top left corner. Plz Help!

Whenever i enter a game my screen starts off very small centered on my screen in windowed mode. In-Game I hit <alt> + <enter> to go into full screen mode. Instead it keep the size of the screen and puts it in the top left corner. I cannot find a fix for it. I tried changing the resolution in-game, all it does it make it worse.