The game is 4:3 and your screen is 16:9, if you want the game to fill the entire screen the aspect ratio on the game would have to change and everything would look quite weird and it would also affect the scaling of the putting grid, you would not like that. Maybe one day they make wide screen versions, but currently those bars just indicates that there is nothing more to show in 4/3 format.
I never use the in game full screen button, instead I use F11 (maybe Windows have a different key) to make a proper full screen. In this mode you do not have to "exit full screen mode" to chat or whatever the in game full screen doe not allow you to do. I also find the meter slightly better with F11.
mrgain:Hi, Ive just had my computer upgraded from windows xp 32 bit and running google chrome to Windows 7 ultimate 64 bit running firefox. My screen is 458mm x230mm. When I come on to WGT to play I find that there are 2 inch black bars down the sides of the screen which cuts the view down to half size.