LoL Big Screen Glitch ( Border-less )

So first off when I would log into the game its perfectly normal. Then after awhile when Im done with a game LoL would get huge on me, making me not see the border of LoL and not letting me see my friends list. This is a problem because I would always have to relog and I can never see in any of my friends invited me to play a game or if they just message me.