Skill is something that can't really be communicated from one person to another. Ya, changing sensitivity may help but the only thing that will really help is experience. However, I use a PC contoller that has longer analog sticks (FPS Freeks work in the same way) and that actually does help. Also, there are ways that you can connect a mouse and keyboard set up to a PS3 (using a third-party product like the EagleEye) and that will DEFINITELY help your aim (WAAAAYYYYYYY more than even obscene time playing).
Wipe that smile off your face and get your tryhard face on!!!
I am serious. The M9 is THE best weapon, in every single possible way. Just CoD it out.