ORIGINAL: kickin_buck
If you have one single arrow this is shooting 2-3 inches left every time, I think I would take care of that problem. I sure whould not want it in my quiver knowing that the arrow is not going to hit exactly where I want it to hit. Are you sure it is the same arrow every time? Try numbering your arrows and see for sure if it is the same arrow. If it is, there are a couple of things you can do. You can try turning your nock, I don't know why, but this will some times cure a flier. Check and make sure the broad is tuned to that arrow, blades lining up with the fletchings, good spin. Try a different broadhead in that arrow, see if that makes a difference. Or do what I would do, scrap that arrow. Good luck, I hope you get it figured out.
I agree with most of the above, but do not believe it is important to have the blades and vanes lined up. If the arrow is straight, it is often the insert. If you can turn your insert 1/4 turn that often solves the problem.
Also your braodhead could be bent slighty. If you put that broadhead on one of your other arrows does it now hit off center? But as kickin said a spin test will tell you a lot if performed correctly.....