Your domain mapping is working correctly for me in Canada. After you do the primary blog set up it can take between 24 - 72 hours for domain name propagation to take place throughout the internet. It's not uncommon for your ISP to be last to flush their DNS cache. You can view the DNS changes here > http://www.whatsmydns.net/ What's important during that stage is to be patient.
re: front page error message
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By default the front page of the blog is the only page that will display all published posts on it. As soon as you publish a post not a page the error message will be gone. http://en.support.wordpress.com/post-vs-page/
For creating a post see here http://en.support.wordpress.com/posts/#publish-a-new-post
For creating a page see here
For editing see:
On the bottom of your Admin page you will find a link to the Learn WordPress.com blogging Tutorial prepared by Staff. http://learn.wordpress.com/
The support documentation is all found at the Support link http://en.support.wordpress.com which is also on the bottom of your Admin page.