It may be a McFarlane ... does the knob rotate left and right??? If so, you likely have the vernier McFarlane throttle.
Also as previously mentioned by others, the carb springs also make a big difference. My original Rotax springs were removed and replaced with the slightly weaker McFarlane springs when installing the McFarlane vernier throttle. I had very little throttle creep with those springs ... but there still was some occasionally. Sometimes I can see the locking ring rotate a little if it is not tightened down enough and the throttle will begin to creep forward. I've recently installed the new Van's helical torsion spring and like them.
Even if your throttle is not the McFarlane vernier unit, you should seriously consider replacing the Rotax throttle lever springs with the new Van's helical torsion spring. The longer stretch springs have had a long history of breaking ... I don't see that happening easily with the new Van's spring.