did you check your tail servo is moving in the correct direction? RIGHT RUDDER APPLIED = SLIDER MOVES TO THE LEFT (toward the tail shaft).
and as in Lees vid..... CHECK YOUR GYRO DIRECTION IS CORRECT
http://www.rc-help.com/showthread.php/7064-Gyro-amp-Tail-servo-Direction-Set-up
1. Check your mechanical set up is centred
2. Check your Gain is high enough.... 65 - 70% is a good start.... get that tail wagging .... put it down and back off 3 - 5 points take off and try again ... until it stops.
The quickest way to check your tail is in HH mode ... pre every flight .... move your rudder left to right and left .... and release. If your rudder instantly returns to the centre.... you either are in Rate mode or your gain is set too low and it is not locking any heading at all....
Here are my tail tips and pre flight checks vids:
Right with that said ... must prep for todays flights !