No need to buy anything.
As I do not know what set you have a bit hard to comment but if I do anything it's very minor e.g. thin plastic cut from a milk bottle.
You can also shim the mast to fuse, which is a better solution as it does not mess with the stab to wing angle of attack. If you shim the stab you are creating the potential for a less smooth ride and reduced glide because you are countering the lift with the flight of the wings and then countering that with your CG.
The following method leaves the AOA of the wing combination the same but moves your CG in the direction you need to feel balanced.
In aircraft terms, shimming the stabilizer is like applying a bit of up elevator through the controls, then moving a bunch of passengers forward to counter that lift and keep the nose down. There is disruption to the airflow.
This method is like establishing trimmed flight for the wings and stabilizer in their neutral state (smooth), then moving passengers around to find the right center of gravity.