cant save mupen64plus changes

[buggasauras]

Hi all,

Im new here, just recently set up my Recalbox and im having alot of fun with it. However whenever I launch an N64 rom it appears windowed (640x480). As a result I have tried to edit Mupen64plus.cfg and change the screen height and width. But when i do this and relaunch, all changes i made in mupen64plus.cfg have been reverted back to how they were (640x480). Ive searched all over but cant seem to find a solution. Any help is much appreciated

Thanks