Thanks for the vivid imagery of your morning BM.
I have ass burn sometimes too. I think it's due to the foods I eat or if my crack is dry. I use a&d ointment or calmoseptine so calm the burning. My crack has healed finally and I don't have burn anymore.
I highly doubt you have to worry about cancer so just try to take it easy until your scope and everything will be okay. I thought I had cancer for sure before my scope a few months ago. I had lost about 20 pounds and was terribly anemic. Guess what? I was fine. I put all the weight back on now...