I agree with advice from previous posters.
I had the same problem with my horse but he is a 14 yr old broke beginners horse who is an ex kids barrel horse. Well at least that is what he was sold to me as. I had the same rushing problem your describing so I feel your frustration and my horse shouldn't of had this problem. I got some help from a friends who breaks in horses and the problem has almost completely ceased at the trot and we are almost ready to start canter work.
So don't get too upset it will happen eventually I sometimes find just stopping and yelling at the top of my lungs or laughing really hard helps. But I ride alone and have no one to stare at me.