Having troubles with plane trim mesh after fatten function

RandomCurveSeam surface.gh (45.2 KB)

Hi everyone. I am a beginner and not a programmer. I am using the Parakeet Random curve seam function to generate a set of lines then I want to make a surface from these lines. I have been successful using multipipe/check for surface normal/flip needed ones and also had good luck with the Dendro/quad remesh but when I try to use the Fatten function I am able to make the geometry whole, but when I cut it with the x-y plane I am getting kind of a mess and I have not been able to fix this.

Any ideas? Thanks in advance for your help.