It doesn't surprise me that you need the weight. With experience, you can start removing some of the weight to shift the CG back a bit. This will make the plane a little more aerobatic, and you will be fine. Even if the plane is designed to balance with a particular engine, is is a simple fact that beginners will over-glue joints, and that there are alots of glue joints in the tail area. The tail area has a much greater moment than the nose, so a tiny amount of extra weight at the tail requires a lot of counter-balancing weight at the nose. So, my guess is that you went very slightly "heavy" with the glue at the tail. This is not a problem.

gus