I was having terrible troble with sddm and kde not working nicely with my monitor. First, get the displays the way you want them. Then all you have to do is type in the below. After doing that you just need to cat the results inot Xsetup and save and reboot.
autorandr --save default autorandr --default default autorandr --force --dry-run default sudo vi /usr/share/sddm/scripts/Xsetup
The last command simply saves things to Xsetup.