Ghost on AWS 404 Waiting on subdomain propogation

I followed this tutorial here: https://www.jerney.io/hosting-ghost-on-aws/ while cross referencing it with the official Ubuntu install.

I got all the way to the end but when I visit my ec2 base url I get the “Welcome to nginx!” page, but when I add on ‘/ghost/’ to the url, I just get a 404.

I discovered this other topic which points out that for some reason you can only run ghost via the specific URL you install with. In my case, I want to host at admin.mydomain.com which I’m pointing to the IP of my EC2 instance. https://mydomain.com points to a website hosted on netlify. It’s going to take ~48 hours for the subdomain to propogate (Google domains gave me this notice).

Is there really no way to start using ghost until I get my domain configured properly?