Hi, I'm Dawid from Poland. Recently I've been working on my English and I'm not fure if my ability to use grammar (and all the other linguistic stuff) is on right level. I would be grateful if you can help me and check that short story (never mind about weak plot).

When the classroom was opened, everybody went silent. Suddenly, a wise-looking man walked into class, and introduced himself as a “somerandomagency” agent, then he took his briefcase up on the table and begun to look on the class. At first I didn’t know why he was there and what’s happening. But I felt that something big and evil had to happen, and it’d taken place recently, he wouldn’t had come for no reason. Then, when I was in the middle of thinking about the case, he suddenly started to talk:
- I’ll go straight with you. We are certain man, Marco de Franco, pervert from Monterray in Mexico. He’s been seen in neighbourhood and we suspect that he is looking at you, thinking about his next target. So from now on you’ll go straight to home after lessons. Truancy is not accepted anymore, if someone do that, he’ll be expelled from school. Did I make it clear to you?
Then, he showed us a slides of this man, and set us free to go home, under one condition – we were supposed to go back in groups. Everyone had done that, there was only one exception – and it was myself. I thought to thyself “What could happen to me? Even if I would met him, he won’t catch me. He would do that If I were one these sloppy, fat kids, but I’m not”, unfortunately I was wrong... I’d met that man in a park. He started to run after me, I wanted to escape, but my legs was petrified and went completely useless. He punched me, and began to pulling into dark place... but then my luck had changed – a police officers were patrolling park area, and they heard screaming... I was saved, but I had my lesson – since that moment I’ve always listened to adults advices.