Hi - I guess you've written a story by now so it'll be about refining it for real exams but I thought I'd write back anyway. At my daughters school they were told to set their story in some other time or culture if at all possible, and then research it a bit as well. She wrote as story about an American Indian and started with the line: "With every excruciating step he took, Chngachuk knew that he was dying". I think that first line really helped so maybe you could play around with some 'first line' ideas. Don't laugh but I'll try to think of a couple - you'd have to provide the setting-
Miles from anywhere, she sat down in the dust and considered her position. By any analysis she was nowhere, but she had been 'somewhere' and that was overrated, so 'nowhere' sounded good for now.
He looked down at his feet. Here was the problem. If only he could get one of them to move, just a step, just an inch, just a hint of moving forward, he knew that the rest of him would follow.
With a certainty that she had not felt before, she knew that she was headed in the wrong direction. She picked up her backpack and whistled to the dogs.
The other thing is to take a theme from another subject so she also drafted for example: Tutenkahmun's journey through the underworld after tht tomb is closed. Also I don't think it is a real problem to write about someone your own age but don't set it in your own culture with contemporary issues.
I heard an idea once of a story about someone who has a phobia of outside, trying to just walk to the letterbox - I thought it would be a great idea but she didn't use it so it's a possibility.
Good luck.