Cannon of mordar

You summon a cannon next to you that shoots one cannonball as far as you can see. Upon firing, make a spell attack roll. if it hits, then the target takes 5d8 bludgeoning damage and 10d8 fire damage as the cannonball makes contact and explodes. You may use this cannon once every turn as long as your concentration last and/or up to one minute. For every additional level you cast this spell, deal 2d8 more bludgeoning damage and 2d8 more fire damage.