Hi. I'm Ken.
The fix is rather simple, and involves use of a couple of hand tools, CA and strip of matching covering. Ok?
At the intersection of the counterbalance and stab leading edge, slice the balsa sheeting on the bottom with a razor saw , in a straight line following the leading edge straight out. This cut will normally remove about a 1/64" material from the cut zone in itself. Then push the gap closed, tape it and check with the elevators in neutral. Generally you will find that this initial cut removed enough material to bring the counterbalance into correct relationship with the stab when at neutral.
If the first cut was sufficient, then wick some thin CA into the slice and I then add a 1/2" wide strip of lightweight glass cloth over joint CA'd in place for strength. Light sanding, then a strip of matching covering and your done. If more balsa has to be removed, take a straight edge, draw a straight line the required distance from the gap, and use an emery board drawn thru the slice once or twice. Usually finishes the task nicely and keeps things straight and lined up when done this way.
Try this, it will work for you if this is your problem.