I tried to create an account but it didn't work for some reason and I accidentally created another one and when I tried to log in, I got a message saying: Multiple accounts are not allowed on one IP-adress. Can I still join or not?
Yes you can. You're just stuck with the first account that you successfully logged in with. If you lost the password for it, request a password reset. But before you do that, remember that USER NAMES are case sensitive... if you typo your username, you cannot login.
Ok, but I haven't logged in yet because I couldn't log in with my first account (probably just typed a letter wrong or something, I should have tried again before making a second account ) then I made a second one and now I can't login with any of them.