It can take a few hours for the DNS check to go green.
And you should only ever need to click the setup CNAME button once. The reason the check doesn’t go green immediately is not because the CNAME records were not correctly added, it’s because DNS changes can take some time to be visible everywhere. And if the problem is that changes take a while to take effect, then making the changes over and over again will not help.
I see you submitted this to Informal, not Community Guides, even though it looks like a guide. But I can tell you it will be rejected if you submit it as a guide, because we already have an official article here: