Being anxious when getting blood pressure readings at the doctor is actually a thing. They call it "white coat hypertension." When I had high blood pressure, my doctor told me to take it several times a week, record the numbers, and average them out to get the most likely accurate overall picture. I actually bought a home electronic blood pressure cuff because mine was dangerously high and I had to send my readings into the doctor, but you can probably find those free blood pressure taking machines around the pharmacy section of grocery stores and Targets.