Why cant I close the end cap on these simple surfaces?

[simon.dyer]

Ive tried lofting, extending and trimming ( crashes Fusion).

Help please - getting frustrated.

Ive deleted the original scan so there are some warnings but not related to the two surfaces

[jhackney1972]

Do you want the indicated area closed in with the rest of the face?

[simon.dyer]

The cutout is deliberate.  I want to close the ends of the two surfaces.

[simon.dyer]

Further to my initial message, admitedly this is my first time modelling using surfaces - I usually use solids but often get into trouble with complex lofts, so thought its time to learn surface modelling.  I watched the very useful video on 3D sketching and surfacing found here https://www.youtube.com/watch?v=7F2SkJhI2g0 and although there are some strange steps, I thought these two simple surfaces could be joined into a solid.  Im surprised that if I use the extend and trim method, then Fusion crashes.  If I try to loft between the edges where I want to close the solid, I get self intersecting errors.
Is there another best practices method I should be using?

[simon.dyer]

Here you can see the result when I try to extend and trim

[jeff_strater · Accepted solution]

loft is the tool to use.  The problem is the default point mapping is wrong.  You need a rail to guide the loft.  I created two, but it turns out you only need one.

[simon.dyer]

Thanks Jeff !!
You can use the same file if you need it for the crash report (#300914105) using trim and extend method