Small output picture

Hi

I have an RPI3 with lastest osmc.
I connected it over RCA to my car display, but i cant set fullscreen, alwyas small picture
try to setup config and change settings at kodi, without success

hi

i need the 1280×480 for best setup
how to force this resolution?

cant find information about this at
http://elinux.org/RPi_config.txt