Did you register through Facebook Connect and you want not your real name?
Let us to know what username you want to use and we will manually set it. Just reply to this post writting just your desired username.
We also suggest you to set a password to use just in case the feature Facebook Connect doesn't work so you can login witn your password and username (your full facebook name by default, just what it's shown at your post).
Also, setting your email address will be useful to recover your password.
If you didn't set your password and Facebook connect is no more working for you, so you are no more able to login, let us to know at email@example.com and we will manually set a pass for you.