AFAIK, as a demo user you can`t download skins automatically, which means you can`t download other demo user`s skins. likewise they can`t download yours...
Soooo... Do what most of the rest of us have done, and beg, borrow, or actually buy a license, then you`re free from the worry that no-one will see the fantastic skin you`ve been working on for days/weeks/months
...as well as getting the many other tracks & cars in the full game, and making a whole load of new friends, etc