Your lines are straight so it's not wandering or most likely a "stupidfire" issue. It's usually an offset or measurement that's throwing it off and needs to be fixed. Unless the implement pulls to the side, in which case you'd need to fudge an offset to account for the pull. 

If you drive with the 3 point up down and back on the exact same line, will it drive right down it's own tracks? That will tell you if it's something in your machine offsets or if your tractor drives correctly and your imp is off