If I hunderstood your request, you can go to "Options -> Preferences -> Video" and select the option "Remember Pan-Scan settings". Then go in "Options -> Preferences -> Playlist" and for Pan-Scan choose "Auto" (if you want your movies to start in fullscreen mode check the Full screen option).
Once you have done these operations clear your playlist and then open a movie, go in fullscreen (if you didn't check the Full screen option) and the film should be as wide as you want.
Now your settings should be remembered by BSplayer for your movies..
Bye
