Hi bartosh, one way is to do a Construct > Network as in the attached 3DM file.

Often times though it is better to avoid putting in tightly bent corners in your profile curves like you have here:




You can usually get better results by leaving those areas to be sharp and building an initially sharp cornered base shape, then using filleting to round off the sharp edges, rather than drawing all tightly bent transition surfaces directly in your starting outline curves.

- Michael