I had the same problem with my Laptop, i managed it, by adding the resolution to the X11 config file.
open the xorg.conf in a texteditor as root. sudo gedit /etc/X11/xorg.conf
Now look for the section "Screen", i guess the list of resolutions will catch your eyes, you can't miss it.
Now easily add the Resolution you need. This may look like this.
Modes "1280x800" "1024x768" "800x600" "640x480"
Now execute the nvidia-settings
, switch to the "X Server Display Configuraion" panel, choose your new resolution and confirm by pressing Apply.
now have a lot of fun