In order for to view your site prior to DNS propagating, you have to use following temp address for your site :

http://xxx.xxx.xxx.xxx(Ip address of your server)/~username/

Example:If IP address of your server is 127.0.0.1(The IP in your welcome email) and if username of your domain is 'user' then use following temp URL of your domain:

http://127.0.0.1/~user/