Problems with extending surface

Hi guys,

I am trying to make a series of curves just like the hand-drawing line is indicating.

My idea is firsty using the surface to divide domain, and getting curves along the surface.

And then divide the domains evenly into 36 parts to get the points.

And i apply a shift list to these points of three curves and set rectangle surfaces according to them.

Finally, i want the original surface to be split by the extended rectangle surfaces to get those curves i want at the beginnning. But i dont know how to extend those surfaces.

Below is the grasshopper script.

I would be very grateful for any help!
Thanks in advance

Also rhino and grasshopper files…
180504MODELSTUDY.3dm (433.7 KB) (8.1 KB)