I really liked it! It created a really good mood, and I think your teacher must have been crazy to give you a bad mark!
The only thing I have to say is about your dialogue. You've got some nice conversations, but they're a bit confusing to read because of the way they're set out.
When you have two people talking, you have to start a new line for each new person.
ex.
“Adam it will never work, if you try to be a catalyst you’ll just end up a corpse,†pleaded Ashya, she was being held at point blank with a very dangerous looking fusion gun. “That’s right Adam, listen to the girl and put down the laser rod.†Adam withdrew, carefully putting down his weapon. “Good boy,†said the masked man. “City-com will be proud of you, it’s a pity she had to die though.†“What?†Adam said faintly, “She’s not dead though!†“Oh so she isn’t, how about now?†The gunshot followed…
This was a very exciting passage, but it was spoiled a bit by the grammar. It should read:
"Adam, it will never work. If you try to be a catalyst you'll just end up a corpse," pleaded Ashya. She was being held at point blank with a very dangerous looking fusion gun.
"That's right, Adam. Listen to the girl and put down the laser rod." The voice was cool and mocking.
Adam withdrew, carefully putting down his weapon.
"Good boy," said the masked man. "City-com will be proud of you. It's a pity she had to die, though."
"What?" Adam said faintly. "She's not dead though!"
"Oh, she isn't? How about now." The gunshot followed...
That just makes it easier to understand. You should do this was all of your dialogue. Also, be careful with your use of commas. Sometimes you're using a comma where you should be using a full stop. Only use commas where the two ideas are linked.
Anyway, I really liked it. I think the only reason that your teacher could have deducted points is because of some grammar issues, but that can be easily fixed. Creativity and good description are not as easy to learn, so it's lucky you've got those in abundance! :)
Good job.