My site is currently live now with Github Pages. When I try to use https://mydomain.com/ghost it does not work and I am not sure how can I set my admin live so I can use it with my domain name. Would I have to use another platform such as Digital Ocean or can I still use Github?
You can only create static websites using GitHub Pages, so Ghost admin won’t run on the platform. You can use GitHub Pages, but you need to manage Ghost on a local machine, convert it to a static site, and then publish every time you make a change.
Alternatively, use a VPS such as Digital Ocean, Linode, Hetzner, AlphaVPS etc.