What type of bit should i ride in?

for western classes i ride with a short shank tom thumb, my horse is neck reined so it is not like i am pulling on her mouth for her to turn and i barely have to touch the rein for her to stop. But I have been riding in a normal D ring bit for english but she doesn't respond to it only when i am going in a straight line. In my equitation pattern class we were doing fine until I had to stop her. she kept trotting to the out gate before she finally stopped. Although I did still place in the class which was shocking cause there were better horses (I thought).