During the sign-up process, it didn't ask for you to create an Administrator Username and Password? It should have...
Also, the file called "index.html" in the /home/username/public_html should be deleted. You can do so by using an FTP Client, or simply your "File Manager", in your control panel.
If you already did all that... then to access SoHoLaunch all you have to do is point your URL to
http://www.yourdomainname.com/sohoadmin/, enter your login information, and everything else is straight forward. Good luck!