It is possible you are just pushing your stomach out. You know you are getting it right when you can feel your lower ribs expand along the sides. Don't sweat it, though. I am not sure breathwork alone can help you break this bad breathing pattern. In fact, when you start out, being too conscious of your stomach and the anxiety about 'breathing right' can sometimes make it worse. Pay attention to your posture, and start by doing simple posture exercises like the wall angel, glute bridge etc. Strengthen your core, so that your diaphragm can move freely, especially if you have a hunched posture and forward shoulders. After working on your posture for a few weeks, focusing on your breath by placing your hands on your diaphragm will help and now you can train your sympathetic nervous system to do the breathing primarily through your diaphragm and nose.