@Kashaziz...................
Thats not a big issue, its just matter of setting your cng kit, if you know its working and the parts in the regulator and their working, you will easily understand.
The thing is that you are using your kit very first time so the cng pressure reaches to the diaphragms to making them a little expansion, when you stop the car n it cool down, the diaphragms try to strach again, resulting this is not giving the proper gas flow to start.
Remedy: Keep the selector switch on gas, try to start and at the same time adjust mixture screw on the regulator by rotating it clock and anticlock wise. At one point car will start, there is no need to push accellerator (rather it should not be pushed and car has to start).
@Guy4u..................
There is no plunger attached to the accellerator on cng, so what will happen if you push 3/4 time accellerator, there is nothing hope but the technique required to start a car