The new screen editor allows you to customize your screen to fit your display. Your design needs to be in the same aspect ratio as your display resolution.
An aspect ratio is the ratio of the width and height of your dsiplay. Computers will have different aspect ratios depending on their screen resolution. Most common size is 1920x1080 which is a 16:9 aspect ratio.
The new Surface Pro 9 has an aspect ratio if 16:10. In the dslrBooth screen editor, make sure to change the aspect ratio so that it fits the aspect ratio of your device.
When adjusting the ratio you may see a grey bar at the bottom of the screen. You can adjust the items on the screen so that the grey bar no longer shows. Check out the video below on how to make these changes.