Using a round pen correctly is an art and a science. There are probably 100 ways to do it wrong for every right thing you can teach. I am now seeing so many problems in horses that come totally from misuse of a round pen that I am not sure any more just how much value they have. I know a little knowledge on how to use one is dangerous. I do not think you can learn how to use one from a DVD or from going to a demonstration. Like everything else we do to teach horses, feel and timing are everything and how and when to apply pressure and how and when to release it is not a quick, easy teach. Something has gone drastically wrong with the application of pressure by the OP.
I have always maintained that round pens are for people and not for horses. There is nothing that you have to have one for. Good interactions with any horse are rewarded with good behavior from the horse. When a horse starts becoming more difficult and his behavior is going downhill, the person 'working' the horse or the methods are to blame.
More horses have people problems than people having horse problems.