Add thickness to gyroid-structured surfaces

I am making a gyroid structure for 3D printing.
I really wanted to make it using Grasshopper’s plugin millipede, but I got a crash error when I installed millipede, so I gave up and modeled it manually using this video as a reference. However, I only made the surface in this video. Since I want to 3D print the final product, I would like to add thickness to the surface, please tell me how to add thickness evenly to this curved surface. Thank you in advance.

Below is the file.
gyroid_3d.3dm (11.6 MB)