Here's a few tips:
Don't "use HTML::Template" - it's already included by CGI::Application.
Don't "use CGI::Session" - go with CGI::Application::Plugin::Session instead (it's a wrapper around CGI::Session that makes using it inside CGI::Application easier)
It looks like you're only using FormBuilder to do a login page - take a look at CGI::Application::Plugin::Authentication. It includes a nice, ready-to-use login form, which you can customize in a variety of ways, OR ignore and write your own - but all the technical details are taken care of for you.
Take time to study the CGI.pm documentation - you have lots of raw html in your print statements - not a good idea.
Some of these modules may have a bit of a learning curve, but they do much of the heavy lifting for you. If you ignore them, you'll be "reinventing the wheel". Good luck!