can't double boost at all

[ROFL Copter]

whether i play with my keyboard or my xbox 360 controller, the double boost just doesn't work
i keep mashing the X button on my controller but it's doing absolutely nothing
i've scoured through multiple discussions of people having a similar issue, but none of the solutions seem to do anything
i genuinely can't figure out what's wrong in my case

UPDATE: ok, so i've figured out that apparently i'm only able to double boost if i move my left joystick around instead of mashing the X button for some reason?? it doesn't make any sense especially since it says on screen that it wants me to mash X but whatever, at least i can double boost now

[ROFL Copter]

update: so i'm finally able to double boost, but only if i hold my left joystick to the bottom left while i mash the X button