Sanyo CE28WN6-B help?

i need help with my Sanyo CE28WN6-B tv, i'm having problems with the screen, instead of it displaying full screen as it should, it shows rounded edges on screen about an inch from each side, radiating inwards, kind of like an hour-glass shape, i was wondering if there was anything i could do ie. commands on the remote control etc to fix this, or will i have to take the tv apart and try and push the crt forward so that it will display full screen. any ideas?