Paranoia man is back

I went to an Urgent Care center to get a Tetanus Booster. The good News first
It was only $61
The shot didn't hurt, it is good for 5 years
I described how I felt to the nurse, she didn't seem concerned.
My temp: 98
My pulse: 76
My blood pressure: 110/80

Now the bad news. If I already have contracted it, I've got it and the booster won't help. The nurse didn't seem at all concerned though, so...