The Symbol Editor in this issue of SuperSpice has some limitations, but nevertheless should allows a large number of symbols to be created. Its principle limitation is that curves/circles are not yet supported. Straight and angled lines, on and off grid and pins are supported in this version.
Existing symbols, that have curves in them cannot currently be re-edited. Support for this is anticipated for this in the future.
Make sure that the first line drawn stops and ends on main pin grid points.
See also Symbol Editor