Thanks for the response!
I’ve asked around and most others seem to think the same (that I’ll have to redo the initial path as a rectangle and bend that rather than a single path (line) with an offset path within the shape layer.
This is just created within AE using a 3D camera. So it’s the same path in a different shape layer moved across to create depth.
I’ve taken these quick screenshots- not sure if they’ll be of any use but it’s worth a shot! If not I guess I’ll just have to redo it :(- you live and learn.
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The initial path- I just edited the anchor points to create the bend/curvature of the plank.

The same path ‘offset’.

What I hope(d) to create- in this instance the top face of the plank by connecting the top lines from the offset paths.

Hopefully that gives my issue a bit more clarity, even if there’s no solution with how I’m currently working.
Thanks again!