Do I need to keep my teeth / jaw lined up?
Most people can NOT maintain an even tooth alignment. However the goal is to take the load off of the top lip and give more of the mouthpiece weight to the bottom lip.
Everyone CAN do that.
Some by a slight forward jaw movement, some by relaxing the jaw and letting space occur between the back teeth (which moves the jaw forward) and some by using a horn angle that releases the top lip so it can freely vibrate.
Never do anything that is painful or awkward. It won’t be worthwhile.