When arms stretched to max you are full of air. Lower arms while holding in breath, then release air when arms are down. Learn art of respiration at home. It will be related to the music by brain and body. Remember what it looks like not feels like.
Feeling can lie.
Breath to expand not expand to breath. Nerves can get best of us. This combined with shallow breathing can be real problem. Standing posture is best to move air. It diminishes till supine position Posture effect inhalation not exhalation.