Ah, that's not a naked domain; that's a naked subdomain, which should (the operative word) be easier. For your DNS, there should be a CNAME for www.at.tutorial-internet.com. Is there a matching CNAME for at.tutorial-internet.com? If not, add one and see what happens.
The tricky part is seeing if ghs.google.com will respond to it.
By the way, is tutorial-internet.com Google hosted as well? Or is it just the subdomain?