Why is my right vertebral artery smaller than the left? could this cause problems?

No: It is not uncommon for the vertebral arteries to be different in diameter. Nothing to be concerned about.

Normal: This is a very common finding. Vertebral arteries are typical referred to as right or left dominant. This reflects one artery larger than the other. Both of the vertebral arteries join to form a single artery called the basilar artery within the brainstem. Having one artery that is larger than another has little overall impact and is a normal finding on radiology or angiography studies.