I had a cardio check up prior to a knee surgery. I got a high BP reading in the first visit with this new doc and he put a diagnosis of HBP on my chart despite my protest that I've always been 110/70 ish prior, even two weeks before that at my PCP.
When I had to go back to the cardio 2 weeks later, I made sure to tell the nurse, no, I'm not doing the BP the second I get in the office, and not sitting on that bed thing with my legs dangling off the side. I'm going to sit quietly in this chair while you do other stuff...THEN you can do my BP. I still read on the high side (130/85). The doc was actually insulted that I suggested it was white coat, and not a pattern, given my own prior readings.
I got my own cuff, test once a month or so (i'm fine), and I never went back to that doctor.
If you're really concerned you might have high BP, get a cuff of your own and test weekly and track for a while, then take those results to your next PCP visit.