I don't think anybody would look down on someone for having incomplete projects on their GitHub.

If they are truly projects you would never need to look at again and they don't add any value to your GitHub you can always delete them.

If you may want to reference them in future but want people to know they are not actively being worked on you could always archive them.

I would also make sure that your pinned repositories on your GitHub profile page showcase your best work as that's probably where anybody will look first. More about pinning repositories

"The problem is that I'm don't have too much focus and I jump from project to project without finishing anything!"

You may want to try working on smaller, simpler projects as they tend to be quicker and you might be able to finish them whilst you still have momentum. Nothing beats the feeling of completing a project and pushing it up somewhere for the world to see!