Recently some people have been receiving an error message when using the CNAME alias method described here: https://www.blogsbyheather.com/2009/10/domain-forwarding-without-the-www-prefix-in-typepad.html
The new method (if the above does not work for you) is to go to Forwarding and setup the forward of the domain without the "www" to point to the domain with the "www". So for example:
forward to: www.blogsbyheather.com
Save changes. Wait for the change to finish. You're done.