Meditating

So a few days ago, our class tried some meditation by sitting on desks and listening to a recording of a "Chi Master" as the lights were turned off. For the first few minutes, I was pretty into it, as I tried to follow all the motions that were instructed and I had no problem. But after staying still for a while, I began to become fidgety. Maybe it's just me, but I can't be still for too long, or else I become restless. But first, I sat still, put my hands in the positions instructed, and so forth. I think that I wasn't able to stay in the position for too long because I don't think I was doing correctly, and therefore wouldn't get anything out of the meditation. I felt as if I was not only becoming tired, but my back became sore from sitting in such a motionless position and I also didn't think that I was actually achieving anything. So for the rest of class, I sat on the desk with my feet dangling and stayed quiet. I would try meditating again, though, if I knew I was doing it right.