One thing to be cautious about...
Your block of wood is presenting an end grain towards the pickguard screw.
I advise you drill a pilot hole for the screw that is the diameter of the screw core before attempting to fit it. In addition, make sure the screw is waxed and even then be cautious when you tighten the screw. If you do all of these things you might avoid the grain splitting.
Good luck.