RE: How much cant?
I think you should cant at the same angle you point . What I mean is, with your bowhand point your pointer finger at something. Now place the bow in your hand and keep the same angle. The arrow takes the place of your finger.
As far as your arrows have been creeping off center thing, You better check your anchor. It will change where your arrows are hitting alot. A tiny bit at your anchor is a whole lot out there.
Bill