When an image or video is not the same resolution as the project’s Video Mode, Shotcut scales that media to the Video Mode max height or width.
I presume you mean 985x849. In the Custom Video Mode, it will round up for odd numbers entered. You may not have entered the same for “Aspect ratio” since the size you want is not the same as 16:9. So my Video Mode is 986x850 for both resolution and aspect ratio.
Since we do not have an example, I made one up from this image.
In Shotcut, just apply the Size, Position & Rotate filter. You will need to keep zooming out and reposition to find your correct settings.
Exported frame: