Problem bending surface after screw tool - what is correct way to extrude?

Hi all, I have this surface that is worked with screw tool in order to have a spiral, following section:

image

after screw tool this is my result with setting I need:

Now I need to bend last surface in order to have it pointing along Z, so I use 9 extrusion using local normal, with rotation on X with steps of 10°

This is my result:

As you can see, surface is bended along Z but, instead of following surface of spiral, it goes straight.

So I did an attempt adding some rotation not only along X but also alog Z (6°), also in this case result was orrible.

How can I modify mesh in order to have last portion of surface, what I have bended along Z, that follows external shape of spiral?

Thank you very much!
Francesco