The Not found status on your hostname is most probably due to the site not being live. You’ll have to share more from your discourse-doctor log.
Does the rebuild/bootstrap complete successfully?
If the EC2 instance is underpowered then there is a chance that discourse would take some time (~3-5 mins in some cases)
What you should be looking at is if your build completes successfully then with docker ps verify that the container is running and listening on 80 & 443. Once that’s verified, the problem is with the AWS security group and not the install itself.