The page you are looking for might have been removed, had its name changed, or is temporarily unavailable. Please try the following:
I am not experiencing a Page Not Found error on my side - your page appears to be working just fine. If you just recently set up the CNAME for your custom domain, you will probably just have to wait a little longer before it will work for you.
Anyone who is visiting the domain for the first time (me for instance) will see a working page, but since you tried to visit the before the CNAME was fully working, your DNS will have cached that failed result and that’s what you’re seeing now. Your DNS should refresh its cache shortly.
Hope that helps explain things.