I opened your file and everything is ok.
if you bake the file, the geometry is as it should be. To display geometry in rhino and also the gh preview mesh is used, and therefor always a visible deviation. your geometry is good and your gh file ok (except for the useless sunion at the end, once capped its a closed brep)
Given the size of object you are designing, are you sure you really need the “Small-objects mm” template? will this be produced at 1/100mm? The display mesh will probably be a little better when adjusted, but at the end it doesn’t change the fact that your model is ok as it. Just “displayed shitty” when you zoom to 0.01mm
I don’t know Tekla, but if it works with mesh, it seems normal to me that you cant have a round edge.
hope this helps