better is a autostart script...
#!/bin/bash
xrandr --output VGA1 --mode "1280x800_75.00" &Save it as autostart, or autostart.sh, and store it under Autostart folder in your home directory.
Make this script executable, right click, properties, permissions, Make the file executable.
If you use LXDE, then save it in a another place, maybe ~/.local/share/autostart.
Now generate a desktop file aka
[Desktop Entry]
Type=Application
Name=xrandr VGA1
Exec=~/.local/share/autostart
NoDisplay=true
and save it in autostart folder.
Logout/in, and it should work.
The best on this script is, you can add other commands as sample a old command (not longer needed)
wbar -bpress -above-desk -vbar -pos left &
Good luck