I have been working on this model and was very careful about start and end points. I ran the solid program and got this help me understand what to do please.
Very hard to tell unless you attach the model for us to look at.
How do I do that
Use the Download option found under the top left hamburger menu to download the .skp to your computer then drag and drop it into a reply window.
Here’s a video on how to do that in SketchUp Web. It might be similar in SketchUp Shop, but I’m not sure.
Hope this helps!
Jason