Is 'kresov@mmk.hr' your email address. If so, then that is why you can see the BCC.
BCC (Blind copy) is supposed to stop the reader seeing who the mail was sent to. But if you are reading it then it doesn't matter if you can see your own email address because you know it was sent to you.
I'm guessing you want to swap those TO: and BCC: values around.
$to="To: kresov@mmk.hr\r\nBcc: Jadranka Newsletter system";
On the assumption that you want a copy of the email to go to yourself, and the rest send blindly using BCC: