I have the same stick, but not in use right now. It was a very stable stick and my first twisty - rudder stick.
It does sound like you forgot to move the throttle lever to full open and completely closed while calibrating. Also, remember to move your twisty full turns in both directions. I find that I get the best results if I move the stick in complete circles making sure to hit the extreme corners first, then turn the twisty motion back and forth a few times, and lastly I move the throttle lever back and forth a few times, ending with the joystick positioned in the center position before I click okay to end the calibration.
PM me if that does not fix the problem.