Saving screen resolution - F15

[Emile]

Hello Fedora friends,
The system starts automatically with a screen resolution of 1680x1050.
I prefer 1280x800 and would like to save it as default resolution.
When I click on "saving as default, it displays the message resolution saved, But in fact it is not and resolution 1680x1050 (auto) is always in the list .
Would anybody have a solution?

Thanks in advance !
Emile