There is, unfortunately, one variable which is beyond the control of both you and your election official--and that's the postal service. Once you leave your ballot with a postal carrier and until it arrives at your local election office, everything is in their hands.
If you haven't already done so, please contact your local election official to make them aware of the situation; they can report the problem to USPS. Also there have been instances where ballot tracking shows that the ballot isn’t delivered, but the election office has actually received it. To contact your local election official, go to the Election Official Directory, choose your state and voting region, and click "submit." On the following page click on the tab labeled “Election Official Contact Details” for contact information.
Beyond that, we can only suggest that you request your ballot as early as possible for future elections, and return it as soon as you get it.