I didn't buy the domain mapping upgrade from WordPress.
The domain helper confirms
No Domain Mapping Found
There is no domain mapping upgrade for lastdayofapril.com. If you would like to use this domain you will first need to set up domain mapping. http://en.support.wordpress.com/domain-helper/
WordPress.com does not domain map free of charge. if you already have a domain that you registered elsewhere, and you want to map that domain to your WordPress.com blog follow these instructions http://en.support.wordpress.com/domains/
Note: After you make the domain mapping purchase and do the set up it can take between 24 - 72 hours for domain name propagation to take place throughout the internet.