I can't say much about the Moon's shape, but you can't convert textures just like that. Use the pltex program included with Orbiter, and refer to the API guide for instructions. I imagine that's the source of your problem. :tiphat:
You created a level 1 texture this way, so the weird polygon is normal in this case.
You should use pltex to make .tex files from bitmaps. Renaming .dds to .tex isn't a proper way to create planetary textures, as it will create only level 1 texture (or maximum level 3 if you copy 3 .dds files to single .tex file - higher levels use patches).