Interesting project you have yourself there
I by no means profess to be that knowledgeable when it comes to the electrics. I did build a few boats along the lines of what you have there - not much beyond that.
I am not sure where you are installing the battery pack but I would recommend installing it toward the side of the boat that is rolling up. This may help offset the torque roll you are seeing.
What prop are you using? do you have other props - a prop with less pitch (a lower angle that will be easier to turn) may tend to roll the boat a little less.
If that is a filter (red) you have installed in the cooling line I would recommend removing it - no need to filter cooling water - it will block and then you will have no cooling.
Keep us in the loop as to how you make out and be sure to take more pics (or better yet - Video!!)
Matt