Questions about Blender 2.9

I have a question about blender 2.9.
I was practicing modeling using Bezier curves

I'm in this state.
The ideal shape is an image like the one below.

I make it with reference to books. Also supports 2.9
Was written. I did everything I could, but
It doesn't work, if anyone knows, please give me some advice.

  • Answer # 1

    I think that you should convert the object of "It has become like this" to a mesh, create the upper and lower surfaces with the F shortcut, and then adjust with Z-axis scaling.