Welcome, Dom!
There is a post here that goes through the steps of creating a bootable, persistent USB drive. It's not recent, but unetbootin hasn't changed in many years. Maybe you'll find it helpful.
The only suggestion I have for the userid/password issue is a re-install. Chances are that you mist-typed one or the other, and attempting to resurrect your credentials would take more time than simply re-installing. Sorry. I've been there, so don't feel bad.