For info, here is the workflow I use in Affinity Photo to patch the hole in the zenith,
after stitching the raw images in your chosen stitching software.
The only thing I add to this is when you make your selection with the flood select tool go to > select > grow/shrink and expand your selection by a few pixels, I usually use +10pixels, this eliminates the need to go around the selection to remove the line(1.40 on the timeline) that is left and gives you a clean fill.
