kaz,
it's clear here that the installer did not perform the operations requiring to get admin priviledge.
The question is, why???
Maybe you should try to investigate why this happened, rather that redoing all the install manually?

Have you been prompted for an admin login when installing ?
Did you give it properly ?
Did the installer not display any error until it tells you to start the web server ?


As an alternative, you may enter in the installer directory from the terminal and sudo the install script ? (it expects one parameter: the absolute path of the installer application directory (the .app dir))
I did not try it but it should work.