Three years ago a had a brain MRI that showed I had a hemangioma on my cerebellum. Dr said not to worry about it. I have been having migraines.?

See your doctor. See your doctor again for an evaluation. Another MRI may be taken. Often migraines or headaches are caused by a fall or accident. Neck or jaw issues often present as headaches. See a doctor that is trained in head and neck pain.
Get a f/u. The important questions are the size of the hemangioma and did you have an mra of the brain? If both the hemangioma is small and no other lesins are noted, then get tx for the migraines..The MRI findings are probably insignificant.