So having built the tail gearbox and tail blade hub you should end up with something like the pictures below.

Check your tail is rotating correctly in that when you spin the main rotors clockwise the tail rotor should spin anti-clockwise when viewed from the right hand side of the helicopter. If it doesn't then loosen your boom and change the 90 degree rotation on the belt to the opposite of what you had before. The tail blades should be spinning such that the lower blade should be rotating forwards towards the nose of the heli and upwards towards the blades. Also make sure that your ball links on the tail blade holders are leading and not trailing the tail blades.