Hi Chipp, sorry yeah just going by your image above and not the 3DM file I thought that your corners were exactly the same radius as the size of the profile curve, making things pinched to an exact single point on one side. But with your upload I can see that there is a little space in there so you should be ok.

Your file is all set to be made into a solid, just delete the bottom face that you had previously built so that you only have the sweep, then select the sweep and run the Construct > Planar command. That will build end caps on the planar openings of the object and join them in automatically so you'll have a solid as the result after running just that one command.

The Construct > Planar command can work in 2 different ways, you can give it a set of planar curves to build a planar surface from (in which case you will need to also additionally join the pieces together with Edit > Join afterwards), or the second way to use Construct > Planar is to give it a surface object that has open edges in it and it will find sets of open edges that are planar, build planar faces out of them, and join them together all in one go which is pretty convenient.

So anyway the upshot is to just run the Construct > Planar command when you finish your sweep and that will get you the result you need I think.

- Michael