I have been prescribed verapamil for migraine headaches & learned later it is a blood pressure medicine. My BP has always been normal. Will this hurtme?

Prevention. The thought is that some calcium channel blockers may prevent future migraine headaches, and that may occur with less frequent and less intense events, but, if there are adverse effects or this fails to benefit, there is botox, other prescription meds, and many otc approaches.
No. Certain blood pressure medications are commonly used to help reduce the frequency of migraine headaches and verapamil is one of them. Most people tolerate it very well with no adverse impact on their blood pressure. You can check yours periodically but more important would be to notice if you develop palpitations or sensations of lightheadedness upon standing. You should be fine, however.
Not unless you . Have low blood pressure. If you have a home blood pressure monitoring device you can check.