Hi Yves, one possibility might be to elongate your path curve so that each piece continued on a sort of mirror image path, then cut them both to the current ending spot that you have now.

But here's another possible way working with just what you have now using Blend.

You would start by cutting away a little bit to leave some empty space that will then be filled in with Blend:



Then slide one piece over so they're lined up with one another instead of offset:



Now select the open edges (you don't want any end caps in place for this, it should just be an open end), and run Construct > Blend to build a connecting piece like this:



Now use that blend section duplicated over (hold down Ctrl and drag it from an edge endpoint for a quick shortcut for this) to get this type of result:



- Michael