[jeisom]

Try adding the following to the screen section.

Option "TwinViewXineramaInfoOrder" "DFP-0"

Alternatively you can run nvidia-settings and under "X Server Display Configuration"
select the monitor you want primary , check the "Make this the primary display for X screeen"
and click apply. Then click "Save to X Configuration file". Use the save xorg.conf file.

HTH