Help everyone I am so worried I have cancer of the anus. Is colonoscopy the only way to tell for sure?

Other options. If you are only worried about anal cancer, this can probably be evaluated with just a digital rectal exam from a qualified specialist. A rigid proctoscopy or flexible sigmoidoscopy can confirm, but a gloved finger should be able to help you. Best to discuss your concerns with a doctor.
Go to see MD. Go to see your doctor and have yourself checked. Your doc can examine and see if there is any abnormality on the anus/perianal area etc. If there is suspicious finding then your doc will refer you to have a biopsy to the lesion, and colonoscopy if indicated- pending to your doctor evaluation- and other work-up accordingly. Dont delay, see your md.
See your doctor. You do not need colonoscopy, but need to consult your doctor. This is not an issue for self diagnosis.