Can somebody please help me understand blood pressure?

So, I am a 17 year old boy, 6 foot 1, and am 140 pounds, and exercise moderately. Anyways, in class, we are doing a lab regarding blood pressure, and upon taking mine, It turns out that my resting is 129/92, and after completing jumping jacks got 106/77. Now, can somebody please tell me, am I prehypertension, or is the device wrong. Is this possible. I eat healthy and only have a fat heavy meal about once a week. Can somebody help me interpret these numbers.