Make sure your bottom and top walls are at least 2mm thick. Print flat (as provided) for strength.
The given dimensions are the maximum size print bed that the stl can fit on. Unfortunately the design doesn't work well with scaling outside the sizes provided. You can scale it but you'll need to create/print some spacers (add a primitive to PrusaSlicer of a cube, and resize it to fit the gaps you find in your scaled print)
After printing, slide top half into bottom half in the middle, and put a plant on it.
** Update 7/28/23 - The 200mm version was over-built for even a very heavy plant. I've refined the shape and reduced the materials substantially, and added a 250mm version also.
The author marked this model as their own original creation.