linuxsudoUbuntuuser-accounts

My problem is that whenever I try using sudo, I get an error message saying: shawn is not in the sudoers file. This incident will be reported.
How can I add my user to the sudoers file? Or how can I log in as a user that is in the sudoers file?

I also noticed, using the "users" command, that there are two users called shawn…
How can I tell which shawn I am logged in as? How can I delete one of them to retain only the user that has administrative "powers"?

Thanks for any help

Find out which id you're logged in as using the id command. This is obviously the wrong "shawn" id as you don't have sudo permissions.
Now, reboot the system. At the GRUB screen, press Esc to boot into recovery mode. In recovery mode, you are root. Delete the unwanted id (userdel) or just modify it to a different name (usermod). Reboot. You should be able to log into the correct id now (id command should show a different uid). If this doesn't work, just reboot again into recovery mode. Delete the other id too. Create a new id and add it to the admin group.