A lot of bipes have that problem. After balancing the wings, a sure-fire cure is to increase the vertical tail area. I would try simply taping on a temporary cardboard extension to the trailing edge of the rudder. Make the extension as big as you like, or try various sizes. If you already had enough rudder authority, just decrease the travel proportional to the cardboard extension area. I think that you will be surprised at the improvement in overall handling and user-friendliness at low speed. Bipes need big vertical tails, for two reasons.
1. They tend to have more wing area than monoplanes, and more wing area generates the required lift at a lower airspeed that reduces the yaw-reducing effectivness of the vertical tail.

2. The vertical tail flies in air disturbed by two wings and the cabane struts. A larger vertical tail is the easiest fix here. I like to use vertical tail area of about 15% of the wing area, and even larger is better, but starts to look a bit funny.