You are still young and learning/maturing in life and at game. Modern day PU is not about thinking of things to say in thousands of different circumstances anymore.
It is about building a better you (inner game) and having outstanding confidence etc I know this sounds cliched and bland but the point is that when you are that better person, instead of saying something interesting (but sounding nervous) it is better to say something generic (but with amazing confidence)
In terms of something you could do tomorrow...I would say, write down all of your perceived drawbacks/faults that are stopping you from talking to this girl/s.
An example would be, a physical fault, like if your teeth were crooked and this stopped you or made you lack conviction when you talk to hot girls
Then set some goals to get these faults to a point where they do not exist or you are comfortable with them! Once you have your list you could then go from there and base all your game and learning on improving them to strengths.