You can be laid back but still be assertive and take action. Being laid back is defined by your attitude more than your behavior per se. Being laid back would mean you ask a girl out and if she says no you are cool with it and look for another girl. Not being laid back would mean you ask a girl out and if she says no you ask her why and start supplicating.
Speaking for myself, I am never nervous on dates, even first dates. No anxiety, no nervousness, and every date is pretty much rambling and bantering about whatever. The girl might not be attracted to me, but the date will be positive and not a freaking interview. To me that is being laid back, despite the fact that I get the girl to laugh and I can be animated.
Don't take being laid back to the extreme of being LAZY or LAME.