has yaw stability issue, correct this and it will fly

It seems that the plane itself has an unusually high wing load, I recommend enlarging the actual wings as big as the whole wingspan of the aircraft, or adding a structural wing and making it as big as the wing shape you made but slightly smaller than the actual wing shape just so that it doesn't protrude outside the aircraft, after all, it's a flying wing type of aircraft. As for the wings flapping when you make them too long, I recommend using structural wings, use overload or xml on structural wings to set allowControlSurface to true, structural wings will never flap even if you make them long. Finally, I tested your aircraft, enlarging the wing will change your CoM and CoL, so you might have to resize the wing to move the CoL, or reduce/add some weight on the craft to move the CoM, just make sure the CoM is in the front of CoL, then you good to go. You also might have to change the airfoil of the wings, set those to semi-symmetric cuz you want those wings to generate lift required for take off