When Im playing candy crush through Facebook, the screen blocks out left of centre and you cannot see the game screen. What do I do?

Hi all, the screen on my apple macair blocks out just left of centre while playing candy crush. I go through Facebook to play the game and the blocking out only happens spasmodically and is bout 3 cms long and 1/2 cm side. It is only on the actually game screen. When I switch back to face book it is not happening. Im afraid that the screen may be not working properly. This is my first mac and have only had it since July 2013. Any ideas???