I think you’ve done an good job of documenting what is a very interesting convective shower cloud. Unfortunately, it doesn’t really work as an artistic image. If that wasn’t your intent, then you did fine. If it was, I think you could have done much better if you pulled off the road and framed the cloud with some interesting lanscape or foreground elements to give it a little perspective. Also, the image looks a bit soft overall, and the trees on the right are really lacking sharpness. Not a bad start though!
I had an image of this type of cloud here a while ago but its not there anymore. I was told by an expert that its an anvil Cumulonimbus cloud, as it rises up and collides into the troposphere, it then separates and spreads across.