Heya Colin. I read your story with interest. It appears that the lesion you describe was some sort of 'milium' or 'degenrative cyst' may have been friction induced. Your description also closely mimics a viral skin infection
which is treated by obliterating it in toto or removing it & is a simple office procedure effected by one of several methods depending on the expertise & equipment at the dermatologist's disposal. Basically, it does not seem anything to be concerned about & do keep your appointment as suggested. Cheers!