Your username can be glitched if it has more than 16 characters or uses symbols (# ! ~ , . | / ect)
Also you should be 100% sure you confirmed email?
If all goes well with registration and you don't get any errors I don't see why it shouldn't work.
All I can say is that in most cases it works, but if not you'd have to check it out again and hunt for a new account.
(Because ingame usernames cannot be changed)