You need to be carefull how you alter the palmshelf, it has to be flat, you can roll the edges off but dont put in any curl. Its difficult to break the rules making an adjustment on a standard Steyr palm shelf which I'm presuming you have so you can pull it up firmly to the base of the little finger.
Its not good technique to put thumb pressure onto the thumb shelf, the thumb cut out is there to allow the thumb to stay clear, the grip should be between the back of the hand and web and the front of the three fingers across the front of the grip.
Its best to discuss this with a good coach so I would do that at your club or if you don't have a club coach contact the county association, they can put you in touch with your county coach.
Good Shooting
Robin