That's the correct URL. I just used it and I did not have access to your Admin section. What makes you think that others do have access to it?
Are you the only official user of the blog? Or have you added other Administrators, Editors, Authors and/or Contributors?
If you are the only Admin on the blog and have seen any evidence of this "access" to your Admin section, then change your password immediately and do not share it with anyone, or place it where they can find it, or choose one that's easy to guess.