Surface trimming error - GSH reconstructs the whole surface

My problem is that I made this surfaces in rhino, then I cropped parts of them and now when I try to use a formula of grasshopper in this cropped surface, grasshopper, somehow, reconstructs the whole original surface.

And my formula for truss making only works with surface parameter, noy brep nor mesh.

Do you know how can I solve this problem? I have my project due for tomorrow.

Thank you so much