As you can see I’m having some difficulty filling in that empty space where the rest of the curve should fill in, as well as including two straights parts to the platform (which are now just two planes attached to the curve).
I’ve gotten pretty close by adding in my mesh (a cube with a simple deform modifier) along with an empty around which I’m trying create and bend that platform.
(As always…) it would be nicer to have the images uploaded here to directly see them and not to do some additional work to help you… it also doesn’t show your real problem because you show the result and not any parameter at all like maybe so:
It’s also seems to be that you have at least two curve objects with different parameters of extrusion and bevels… so if you want to fill the inbetween you may want to copy one curve and use different values for it and may use offset… or even have to make up an in between curve…
But this is just guesswork… because you didn’t showed you curves/problem in an recognizable way…
If you can elaborate… then the changes for a proper answer will increase enormously…