You’ll need to create a “user site” instead of a project site. See Types of GitHub Pages sites:

To publish a user site, you must create a repository owned by your user account that’s named <user>.github.io . […] Unless you’re using a custom domain, user and organization sites are available at http(s)://<username>.github.io or http(s)://<organization>.github.io .

I don’t know if renaming your repository will work, or if you need to create a new one.