Blender Model Not Working Properly

I am making a mini golf game and I made my first mini golf hole in blender. Its a very basic mesh plane with a cylinder going through it for the hole and theres a cube that frames goes around it for the walls. When imported to unity it looks really weird, there’s a bunch of holes going through it and if you look at it from underneath the mesh plane is invisible. I wanted to test it out a little more anyway so I checked off “generate colliders” in the inspector, but my character (first person controller) can walk right through it. Does anyone know how to fix these problems? I tried a bunch of stuff like recalculating the normals in blender but in blender it looks perfectly fine…
Thanks a lot, all help is greatly appreciated.

As for the collider issues, you may want to make sure that the colliders you are using interact the way you think they do using the charts on this page. Also make sure that you actually have a collider attached to your imported objects.

For the plane, you might want to look at this to see if it helps with your problem. You may just be having an issue of the plane not projecting the texture on both sides, and the link offers an explanation on how to correct that.