Registration opens at midnight UTC every day and fills quickly, sometimes within seconds. If you tried last night, you didn't get a slot. Only a few accounts are allowed to be created each day for free. I don't see a partial registration in there for you, so you'll need to try again tonight.
as an alternative, you can also donate at least one dollar and you'll receive an email that you can use to register regardless of what time it is. If you don't receive the email for that I can always resend a donor invite.