And you called before and informed the PO or at least called that morning and informed the person you were to report to.

There was some emergency that caused you to miss and have it in writing and documented.

Or do you have your toothbrush packed ready to be back in jail

That is a question for your PO. They will want to know why you missed it. If you had some type of emergency, they will usually work with you, and not against you. However, if you make a habit out of it, they can revoke the community service, and make you do the time.
Good luck, and God Bless.