Filling the gap / Create solid between 2 curved surfaces

Hi all,

I am fairly new to Grasshopper and I ran into this issue while I'm exploring design alternatives for my uni's project. As seen in the attached, Image 1, I want to have the red and green be connected to each other as a solid component. How can I do so? I tried loft but it won't work. When I loft it, the result is as shown in Image 2. 

This model is started as Lines (Image 3), I have then extruded the Lines to form a curved surface. Then from this newly formed curved surface, I offset to create another layer which I hope to be made into a solid component.