It sounds like you have a history of GI issues so I would suspect something along those lines. If they discovered anal fissures during your exam, then wouldn't that likely be related to the cause of the symptoms?
In my case I had no history of GI problems at all before rectal bleeding started. Blood turned to discomfort, fullness in the rectum, and pain. I went to the GI and got diagnosed. I actually was convinced I had hemorrhoids, but alas, no such luck.
It's understandable to be anxious but cancer in people our age is very, very rare. Usually there is a genetic element to the cancer when it develops early. In my case, I have Lynch syndrome, which means I was born with a broken DNA mismatch repair chromosome.
Good luck with your colonoscopy!