Slab is not projecting properly

Hi everyone,

I’m using Grasshopper, Archicad and Rhino. I drew a polygon shape in Archicad and want to further develop through Rhino and Grasshopper. When I wanted to project a slab that would have shape of the initial lines from Archicad, the shape of the slab is in a left corner ‘simplified’ and doesn’t go along as a curve.

I appreciate any suggestions how to fix the problem with the shape of slabs. Thank you!