FishicallyDumb

So im trying to edit some .stl files to use in cura. Im using Sketchup to edit the file, export as .dae, and convert to stl thru Accutrans3d. This is the unedited file on the right and the edited file on the left. Everything looks good. But as soon as i go to preview to view the layers: Why is this happening and how do i fix it. Also sketchup: Thanks.