It happens to the best of us!
To get a reminder of your username, all you need to know is the email address you used to create the account. If you don’t, it’ll just take you a wee bit longer! (You need to test with all of them.)
On the login page, click the forgot password link,
Fill in the email address you think is associated to your account and hit send.
You’ll get an email with both, your username and a brand new password. (If you happen to remember your password, no need to click the link, and it will remain the same).