I loaded up this game to test specifically for this problem, and the first few shots performed exactly as you described. But then I changed my hand position and it worked properly.
I first used my right hand and spun the trackball (HAPP, iPAC) and couldn't get it to go at that angle without it going to the left.
Then I used both hands, but only my thumbs, resting my hands on either side of the trackball and moving my thumbs forcefully in the direction I wanted, specifically up and to the right. It worked great.
Just wondering if the initial spin detection on the rollers in this game partially or wholly dictates the direction, and maybe it's not very forgiving. I figure using my right hand only, there is a little less force where my thumb is thereby creating the leftward drift.
Any lefties to chime in?