TB or not TB?

I was required to have a TB test, which isn't exactly as fun as going to Lagoon, but really no big deal, right? So I got the shot under the skin and returned 48 hours later for my reading. The injection site wasn't blistered, but it looked a little bit rosy. The nurse lady picked up my arm, scrutinized the tiny reddish spot, then scraped it with the edge of a Post-It note. She rubbed it with her thumb about 12 times, then squeezed it, then scraped it, then rubbed it. She took out a clear plastic strip printed with graduated sizes of circles and held it over the now-much-redder spot.
"Um, is everything okay?" I asked.
"Have you been out of the country in the past month?" the nurse replied.
"No."
She tapped the clear strip against her palm. "Well, even if you had, the mark on your arm would have to be four times as big to be a positive result."
SAY WHAT? All the scraping and pinching when it wasn't even close to the right size for TB?
"I have sensitive skin," I offered. "I bruise and sunburn easily."
The nurse smiled for the first time. "That must be it!" she said, and cheerfully signed my paper signifying I was clean-as-a-whistle. I grabbed the form and dashed out the door before she could decide to inject my other arm "just to make sure."