There are a couple things to consider.
Make sure you retune your bow to shoot 3 under. You want that bare shaft flying a touch nock high and weak. When going from split to 3 under the arrow will respond differently.
Now that you know your arrow is flying perfect there are a couple things you can do to move your impact point to the right.
As folks mention, increase the cant is one.
Going to a softer side plate will also move the place of impact to the right.
Lowering your anchor point will also move it over to the right. The higher the anchor the more left you will shoot.
I have also found that if I shoot a tab I will shoot to the left. When shooting a glove which is thicker and moves my anchor away from my face the lefts will not be as dramatic.
The other alternative is to shoot a bow that is cut more past center. This will help cure some of the left. A good comparison would be a Hill longbow versus an ACS. The ACS since it is cut way more to center will usually have your aiming spot and point of impact directly in line vertically.
I fought with the 3 under lefts for quite awhile. Some folks don't experience it due to their anchor point, bow design, etc. Other's like Allen aka AS here on TG always fights with it to some degree. He is a great resource, don't hesitate to reach out to him if he doesn't respond.
