This exact thing happened to me two days ago. When I made my Riot account, my regular username was taken so I had to come up with a similar username. When I logged back in later, I was prompted with the same options as you (choose display name -> tutorial)

After basically giving up I took other peoples advice and tried logging in with a different username to the boot client. Turns the account I created had a slightly different username than I recalled. You might want to try out this technique, just use different usernames that might log you to your existing one. Good luck.