It is possible that the CG is spot on.....trainers are often blanced perfectly with no weight....but Tom is correct, for an accurate CG reading, get the Great Planes CG Machine....it's a great investment in the hobby.....you'll use it for all of your planes. (except giant scale, which won't fit on it!)

The screw in your vertical stab will work just fine, but you might want to add a rubber band between the screw and the antenna....just to give the antenna some flexing room when the plane is flying.