doesn't matter when you open it, just when youre ingame go to firing range and try different weapons with recoil and see if they work or not, you have to press either 1 or 2 whichever gun you wanna use so that the script knows you selected the weapon, example if you have r99 in 1 slot and flatline in 2 slot, after running the script press 1 for r99 or 2 for flatline, the script has to know which weapon you have equippped, And also check your sensitivity in the settings.ini file, make sure you put in the sens and zoom sens according to your ingame settings.
thats it, try shooting without moving your mouse the weapon should fire straight, well almost straight with no recoil atleast
if you have anything more to ask you can, happy to help