FaceTime doesn't go full screen on my Mac desktop.

FaceTime doesn't go full screen on my Mac desktop.

I am running version 10.9.5.

Last time I used FaceTime I could make the picture go to the full size of my Mac (21in) but now it is not even half that and I don't have the option (two expander arrows) to take it to full screen. I have tried with the mouse and will the side bars indicate they will widen they don't. I have also tried the keyboard. I have looked for the camera settings and can't find them. Its annoying I can't go to a full screen camera.