can I use full screen on my Mac book pro?

Hello,

I have found the option to use full screen in FaceTime on my MBP, and realise I can only use it once a video call is being made (it's greyed out until then), but when I go full screen it's not really full screen, the sides are black and the picture is narrow. I may be wrong, but I'm sure I used to be able to get the picture right across the screen?

Thanks, Sally