How to become a scientist and get a job jn NASA. I know that sounds a little difficult but not impossible. i believe in dreaming high and working really hard to accomplish those dreams.

Way to dream BIG Tabish! The sky IS NOT the limit!
I've had classmates that worked for NASA in Mountain View, CA, Jet Propulsion Lab (JPL) in Pasedena, CA, and an old friend in Indiana, who just applied to be an astronaut, so I hope I can give some insight to the path to achieve your dream.
First step would be to flip through some books on astronauts to discover that astronauts come from many fields of study, from teaching and psychology to mathematics and engineering. It's about teamwork and problem solving.
Second, if you have the opportunity, try to find an activity or group that allows you to practice teamwork and problem solving. I participated in US F.I.R.S.T. Robotics in high school, as did my astronaut friend.
Thirdly, choose a field of study that is important to you and that you find enjoyable. Don't be cornered into something you feel will give you higher chances.
To speak from the engineering side of things, you can study statistics, mathematical analysis (FEA), mechanics, materials, electrical, chemistry, civil, software, computers. It's a huge field. From mechanical engineering, there is a field specifically call aerospace engineering which will closely look at the science of flight (Fluid dynamics, propulsion, materials, etc.)
For reference, the 4 folks I know involved in spacey jobs studied, mechanical engineering, electrical engineering, and mathematics.
IN the words of Mission Control from the very first Moon Landing Mission, "Good luck. And Godspeed!"