There is a problem with the boards we are fixing this.
Until then If you try playing in live premium not live simple, make co-ordinates so they show inside the board not outside, and use the F11 on your keypad, that should make the screen full size for you.
http://live.chess.com/live?v=2011072202#
setting
If you need help, please contact our Help and Support team.
I don't understand why my board small today? I had set it extra large!