It would be shorter, but not narrower, because a dwarf is as stocky as a human.
Talk to the DM, and make sure he understands your plan. You may have to pay extra to get it custom made, (or just buy one from a dwarven smith), or perhaps buy a regular heater shield as a tower shield for a dwarf.
But make sure that you and the DM are in agreement about what you bought while you're still in town. Don't discover the problem during a melee. I also urge you to explicitly say that you spar and train with it before the first fight.
Many misunderstandings between player and DM can be fixed by bringing them up early.