How can I explain the reality of my school curriculum (International)

Answered

So for students who live in the US and apply to colleges their high school will send the colleges they are applying to something called a "school profile." This profile lets admission officers know important information about the high school the student attended. Do you have any idea if your school has something similar? If so, you can see if they can send that to the schools you end up applying at.

This is also something you can include in the Additional Information section of the Common App. It's a unique enough situation where it's worth mentioning and writing up a short, simple, explanation of how your classes worked and you can include information on the additional classes you took compared to someone from the US.

Something to also consider but you didn't mention, consider if your high school transcript will need to be translated. If it isn't in English you might (probably will) need to get it translated. Some schools will accept unofficial translations from an English teacher or something but it may need to be a certified translation. Something to think about as you continue through the process.