I can't seem to use Azir's Ult properly

I'm not sure if it's just a problem with me executing the combo too quickly or if it's just one of the many nuances in mastering this champion. Basically, when I ult, instead of going the direction I want it, it will sometimes go the opposite. This of course is just...aurgh, for one thing, it easily decides whether I live or not. Not to mention humiliating because I just know, I'm going to see that bloody "?" in /all or from my own allies, which is just tilting to the max. Now not to say I completely suck at using the ult, it does go the way I want it to half of the time, but the other half....yeah.