It's not family, but I learned lesson from my classmates -> It's not a lesson I learned from family, but instead, it's a lesson I learned from my classmates

- The important lesson I learned from my classmates is that I should not judge others by their appearance (<<--Perfect, no corrections! Great sentence)

At the beginning of the semester, I judged their personality by only their appearance, but after time passed and I got to know them more, I thought I was stupid in the past -> At the beginning of the semester, I only judged their personalities by their appearances, but after time passed and I got to know them more, I realized I shouldn't have done that / I realized I was mistaken

*If we want to add more to essay (so we can meet those word requirements [e.g. 450 word essay]), then we can give another example of judging someone by their appearance or give an example of a time when you didn't judge someone by their appearance and what happened/and the result of that.

As this experience, this lesson made my way of thinking more mature in my life -> As a result of this experience, this lesson made my way of thinking more mature (***<-- Good! Excellent insight here, Yuna! : )

So I think this lesson is good -> So I think this was a good lesson.

--- Overall, great job on this essay Yuna!! ⭐⭐