Pointing your domains to a gh-pages branch requires three steps.
-
Add the Github IPs as
Arecords on Namecheap.
185.199.108.153
185.199.109.153
185.199.110.153
185.199.111.153 -
Add your Github domain as the
CNAMEalias on Namecheap.your_username.github.io.(mind the extra period!) -
Add a
CNAMEwith your new domain name in your repository. lowercase and nothing else

Explained here https://www.namecheap.com/support/knowledgebase/article.aspx/9645/2208/how-do-i-link-my-domain-to-github-pages