You said the plane will not move until you reach 50% throttle. Make sure the propeller is on the right way. Make sure the flat side is facing the motor, not the nut that holds it on. I think you need to balance it. Pick up the plane with your left & right fore finger under the wing along side of the body where the wing sits on top of the fuse. When you have your fingers located at the 25% of the wing, measured from the leading edge to the trailing edge. The nose should drop 15º. If it doesn't drop at least 15% below level, add some weight to the nose, under the motor until it does. Let me know how this works out.....

Larry