The two fields at the arrow I drew are key: Set the resolution of the 3D printer nozzle to 0.2mm and then set the tile width as large as you can get away with (the website has a size limit so need to pick the highest width to just be under that size)
The STL and gcode file I used can be found at http://git.fenrus.org/tmp/vulcanoes.zip (35Mb download)
(note that not all CAM software can deal with STL files of this level of detail… it might be a stretch for Fusion360)