Entries are "Public" by default. Select "Private" if you do not want your submission to be published. Please also preface your message with the text "(Private)" to prevent accidental publishing...
Warning: Spammers regularly search guestbooks/ comments!! I recommend you add your email with some anti-harvesting syntax, such as 'user at hotmail dot com' (instead of user@hotmail.com). (Even that might not be enough though, so consider who you want to contact you...)