The anxiety is very normal. What you have to do is ask - have I done all I can...?

Did they offer you further treatment and you refused? Or did they say this is all you need?
Are you healthy - eat well, exercise?
Have you healed well?
Have you given up any contributing habits (this applies if you are a smoker or heavy drinker etc... HPV+ cancers shouldn't necessarily be included as they do have an obvious cause, but being healthful can't hurt).
Did you seek out the best facility for treatment, and have top a top notch medical team?
Did you advocate for yourself and educate yourself on what to look for in terms of a recurrence?
Do you attend your regular check ups?

If you can say you are doing, and have done all you can, then you need to let it go. What is going to happen - will happen - at this point.

However I find it curious your dr. said this to you. If he or she believed this then why didn't they offer you more treatment as a safeguard? Since there were other therapies available... Regardless, no dr. knows. So don't let this person's negativity affect you. You are a year out. This is a good thing.

best of luck.