Don't worry, you probably just logged out! It is not possible to delete your account from within the game. Please try logging in to your account again. On the login screen, click "Switch accounts", click the "+" icon on the top right, and then use either the email on the account or the username, and the password you have set. If you can't remember your password, see this article for assistance.
If you're having trouble, feel free to submit a ticket with our support staff. Please use the "Technical and General Support" category for this issue.