Thanks for sticking with it, and sorry for the trouble! You found a real bug: the sign-up form called your password "Strong", but the account server needs a password with at least one capital letter, one number and one symbol (like ! or #), and the form wasn't checking for that. It's fixed now. There's a checklist under the password box that ticks off as you type.
It looks like an account was created with your email on one of your earlier tries, so you may not need to sign up again. Try Sign in first. If the password doesn't work, use Forgot your password? and you'll get a link to set a new one.
And if you'd rather skip accounts entirely, the itch version saves right in your browser with no sign-up needed.
Thanks again for reporting it. It means other players won't hit the same wall.