Just wondering if you're getting the needle through school. At the school the 6s got their HPV needle in the library so I got to see how it goes. If it's through your school it will prolly be a public health nurse who does it. Here is the scenario - you sit down and the nurse will swab the arm, getting you to look away while they give you the vaccine. The needle itself feels like a pinch. Yes there is pain but it does not last long.
If your situation is the same as what I've seen you will get a juice box and told to sit and relax for 15 mins. The nurse will prolly tell you to swing your arm around as it is supposed to help. I have never gotten the shot so I cannot tell you first-hand what it's like but that is just my take on the matter.
I hope this helps a bit. It's okay to be nervous. And of course, ask the doctor/nurse all the questions before and after.