In the U.S. when you apply to college, you specify your major. You are then accepted or not as that major. But the minute you get there, you can change your major.

So I think that's why they are asking you to declare a major now in high school. It must be a similar system.

But do ask your counselor and don't forget to ask how easy it is to get jobs in the field of interest and what kind of salary you can expect.

Good luck on the exams.