the exposure it pretty much correct, your main problem is you've shot from a boat; you might as well have shot hand help as the movement from the boat has given everything a blur due to the slow shutter speed.
next tip; set the camera to manual focus as then infinity, this means the fireworks will be in focus as you've capturing the light trails, this also stops the camera hunting for focus and then you missing the shot
next tip; increase the blacks in PP, this will start to remove the smoke on the photos
next tip; get a remote shutter release or use selftimer, even on a topend tripod and head, pressing the shutter release moves the camera again causing ghosting.
lastly, make adjustments as you shoot, there is no set combination for fireworks so it's trial and error as you can't guess what the ambient light is going to be.
couple of my firework shots
_DSC2454 by
The Ridg, on Flickr
Edenbridge fireworks display by
The Ridg, on Flickr
Edenbridge fireworks display by
The Ridg, on Flickr