There's no control here that verifies that the mysql_query operation was successful. The your post has been added message happens so long as $name, $email and $message are not false variables.
Just looking at this query you have syntax errors:
You have trailing commas in both. Add an
INSERT INTO gb (name, email, message, time, date, ip,)
VALUES ('$name', '$email', '$message', '$time', '$date', '$ip',)
or die(mysql_error()) to the mysql_query function call, or capture it in an if() branch to determine if it was actually successful or threw an error.
BTW, both time and date are theoretically listed as allowed reserved words. That is, they are considered keywords in MySQL, but due to popular use of field naming in the past, oracle has allowed them to go through as unquoted and still resolve to the proper field. You really should rename them or backtick them to ensure they will work in future versions (which they likely will retain the current rule set in anyway).