Stl file doesn't produce a perfect g code file in Cura 5.8

I'm a retired Architect and learning Designspark to replace Sketchup for 3D printed hobby pieces.

A current wind sculpture piece has been my learning path ( a little painfull at 81 ;-)).

I've got the piece done  but apparently have some extraneous faces or other irregularities as Cura slices the thing with some extra faces in the part.