I am not running any screen on my side, so I am not sure how to adjust the resolution. I have seen some discussions of that in the thread for the images that I shared with you previously. I would suggest you search in that thread, as there are some settings shared by other users with similar setup as yours.
If your pi is on the network, you can also connect to it remotely from any web browser (that is how I use mine when I want the Web UI), and it should scale properly to your resolution in that case.
Ghislain