Thank you for replying! In fact I'm using the trackpad on my laptop and it works perfectly in every other situation! It's very strange the way it will just suddenly veer off in this game. I think it must be a bug :-(
My cursor is all over the place. I couldn't even exit the game without using Task Manager. Setting the mouse to less sensitive makes it slower to move but then I still get the sudden jumps, so it's actually worse.