TARS

On the vertical stabilizers, use wings and not structural panels

You'll need to give more info on what the problem is.. Is it doing backflips? If so you probably need to move the CoM in front of the CoL (to view click the three lines in top right, then "show CoM, CoT, CoL") if it's spinning horizontally, then there's probably more complicated problems going on and you'd need to describe it more or post a video (or the plane)

Spinning?