Why is my email stuck in "Scheduled" even thought I sent immediately?
You either need to run the job manually or have a cron that runs periodically that will execute the job that actually sends the email.

In my Drupal install, you find the place to manually execute it at http://www.yourdomain.com/civicrm/admin/job?reset=1

Or:

Civi Menu >> Administer >>  System Settings >> Scheduled Jobs

Some links with more info:

https://docs.civicrm.org/sysadmin/en/latest/setup/jobs/

https://docs.civicrm.org/user/en/latest/initial-set-up/scheduled-jobs/