Good luck with your appointment tomorrow, Brian. It’s always a good idea to get anything new/changing checked out right away. As SK noted, it can be curable (easily curable if caught early), but early detection, especially with melanoma is critically important.
My dad and my aunt had melanoma, and neither one died from it (they died from other, totally unrelated cancers).
No matter what they find, best to trust in your doctor’s care and try not to worry too much. Let us know how it goes when you’re back from your appointment. I’m hoping for the best, and keeping you in my thoughts!