The directions you are given don't ask you to describe a challenge you have "won," but to explain how you reacted to a major challenge in your life that did not turn out as you had hoped and expected it would. You have done an admirable job of answering that assignment by providing background information that tells what you anticipated, explaining what actually happened when you took the SSCE, and giving examples of how you are making the best out of the situation you have to deal with.
I would suggest starting a new paragraph at "According to the educational system of Bangladesh..." since you are moving from background information to explanation of the critical event that became your challenge. You might also want to start a new paragraph at "Now, I am..." as you relate the actions you have taken as you have reacted to your new school setting. You might want to change or eliminate the final sentence.