Not sure if it's what you meant, but I had a similar story where I reacted to everything, even the control. The allergist took that to mean "you're really allergic to everything," but I went looking for a second opinion who was able to get both the positive and negative controls to work. Turns out I'm not allergic to everything, the first allergist just didn't recognize benign dermatographia and was a bit too quick to ignore my positive reaction to the negative control. In all, it saved me a good chunk of change and sensitization risks that would have come from having unneeded components in my allergy shots.

I don't know the details of your case or if any of this applies, but if by chance you were in the same boat wrt the negative control it might be worth circling back for a confirmation test at some point.