This is a perennial problem with websites that you only use once a year!
Now you don't need to worry. Just use your email address to login and that will lead you to the correct account. Forget about usernames! Of course if you cannot remember which email address you used, then try another one. Only in the worst case, open a new account!
And you may well have forgotten your password. Don't worry. Got to the login page, and click "Request new password" just above the login button. You will be sent a one-time password link.
Still got problems? Then just contact me.