As a former probation officer in Dallas, I can tell you that you took the appropriate action once you realized that you overlooked your appointment. The duty officer (the officer assigned to handle situations like these) will take your report as soon as you go in if your officer is out. It is when you miss an appointment, do not call, and do not report that your file ends up in court with a violation report and warrant. Work on a supervision plan with your officer to help you budget and get your fees caught up as you are in compliance with all other terms. Because you are on deferred, your case will be dismissed upon successful completion and you can move to seal it. Good luck.
My answer is for informational purposes.
Ms. Wilson is correct that you did everything that you should have done. You will in almost all certainty not be arrested for missing your scheduled appointment, nor will you face a revocation. When you speak with them at your appointment, be honest about your mistake and let the PO know that you have now scheduled it on your calendar or put the new dates in your phone/calendar with a reminder. Show that you're doing your best for a successful completion.
Although my intent in answering this question is to aid you in the legal process, my answer does not establish an attorney-client relationship in any way. You should seek the advice and counsel of a qualified attorney in your community to evaluate your legal needs and to advise you. No Attorney-Client Relationship is created without the specific intent of both parties.
As you know the Williamson county probation department is extremely strict. This is the county where I primarily practice and I commonly hear complaints from my clients and others about how tough on them their probation officer is being, especially when they have changed from an old officer with whom they have built a relationship to a new officer who doesn't know them.
That being said, missing one meeting while promptly making it up should not result in any jail time.
It is important to remember though that if you give them any substantive reason to revoke you this and all other of your seemingly minor missteps on probation will come back to haunt you. So it is doubly important to make a significant effort to be up to date and on time as well as being caught up on your payments to the probation department going forward.