Need Advices for Appeal Letter (NUS Science)

Hi, seniors, I am an international applicant applying for admission into NUS Science, but got rejected a few days ago. Currently, I am writing an appeal letter. I think that I am qualified to be admitted into NUS Science course. However, I have no idea on how to write a good appeal letter to convince the admission committee. Below is my appeal letter. Could you give me some advices? I really appreciate for what you do for me!!

It was so disappointing to me that I cannot study Science and read statistics in NUS, since I think that I should have been offered a place to read statistics in NUS based on my A-level mathematics result. Being admitted into NUS is so important to me since the things I learn from NUS are essential parts to fulfill my mission. If I can be admitted to read statistics under the guidance of the knowledgeable professors in NUS, I study hard so that I can graduate with a first class honour with a secondary major in Finance. After graduation, I will be equipped with necessary skills to enter the top universities in the U.S. or Europe to pursue a master degree and doctoral degree as well as the CFA designation. I plan to start my career in the financial field after graduation and teach undergraduates in university. I sincerely hope that you can give me the chance to pursue study in NUS and to repay to your institute. Thank you very much for taking your time to reevaluate my application.

P.S. There is a limitation of 1000 characters for the appeal letter. In this letter, I have already used up all the characters permitted.

Keep the verb tense consistent:
It was so disappointing to me that I could not ...

...to fulfill my mission. ---Oh, I like this part. This is a GREAT approach.

If I can be admitted to read statistics under the guidance of the knowledgeable professors in NUS, I will study hard so that I can graduate with a first class honour with a secondary major in Finance. After graduation, I will be equipped with necessary skills to enter the top universities in the U.S. or Europe to pursue a master degree and doctoral degree as well as the CFA designation. I plan to start my career in the financial field after graduation and teach undergraduates in university. This is not a mission! I want you to write about a specific goal you have. What is the real goal of the mission? What is the big splash you will make in this world? You have to read a few recent articles about your special interests in the field, and mention a current issue ... and your idea for helping to solve a real problem.

:-)