Your letter contains many English forms that are characteristic of a non-native speaker but are nevertheless effective in describing your personal situation. A full correction to near native standard would possibly give an inaccurate impression. Perhaps you should contact the university and attempt to gain some feedback on their expectations of the English used for the application.
I don't know if you will get volunteers to work on such a long piece. Perhaps if you post each paragraph separately it will be less taxing.
Here's a few suggestions re para 1
1) This to me is not evidence of a capacity to study economics at graduate level - possibly delete
My inherent tendency for economics emerged at a very young age where I didnít even know that there existed such a word. Even though I was an active cheerful kid, I never was a destructive one who broke all the toys apart.*** I was frugal instead. I still have most of them functioning even after 26 years. I have always been a farsighted decision maker without any influence of my parents at all.
2) maybe Ok - what year? Not terribly rational
My passion for economics sprang up with a school field trip to the Central Bank of Sri Lanka. My dream has been to be a professional in economics ever since.
3) Driven with my instinct > driven by my interest/enthusiasm/passion - instinct is a mainly biological function not intellectual
4) I was a frequent prize winner. > do you specific details?
5) At last my steadfast efforts and fanatical studies really put me on the track > At last my steadfast efforts and dedicated studies put me on the track to tertiary studies - fanatical is too strong - fanatics may be crazy
6) higher Z-score - explain please
7) Very few students - how many?
8) to come to that handful. > bad grammar - suggest: to be selected
Advanced Level examination is the hurdle that one has to go through to enter a university in Sri Lanka. Only about 9% of the students who take the examination get into a state university. Driven with my instinct for economics coupled with my dream, I majored economics in school. I was a frequent prize winner. At last my steadfast efforts and fanatical studies really put me on the track and placed me at the 30th place from the Colombo district and led me to the University of Peradeniya, one of the leading state universities in Sri Lanka. It is the only university that offers a bachelors degree in Computation and Management which requires Economics as a prerequisite and a higher Z-score. Very few students are selected and I was lucky enough to come to that handful.
9) Not sure any of the below is useful as I suspect university is more interested in your intellect than your health
I had just finished the 1st semester of my 1st year as an undergraduate when I was diagnosed with Lymphoma (NHL), a malignant cancer that had infiltrated 20% of my bone marrow. I had to miss my batch to undergo a series of expensive chemotherapy for 6 months, the period I wish I could erase from my memory. I lost all my hair, immunity, skin color, my batch mates and above all I lost one priceless year of my life. When I was struggling alone to start from the scratch, I met this temporary lecturer who helped me to stand on my feet. She treated me like her own sister and stood by me. I didnít have any ideas on pursuing higher studies until I got to know about her plans for graduate studies in the USA. She inspired me. Despite all the hardships I faced, I determined not to give up until I reached my goal.
10) could expand > bad grammar > suggest expanded/increased
11) where students found many difficulties > ...maybe just talk about yourself
12) could further realize my great passion towards economics > I further realized my great passion for economics
13) enhanced my dream > strengthened my dream of undertaking graduate studies
14) knowledge of > not > on
15) was able to explore > not > could explore
16) I took or completed courses > not > I followed courses
17) I have > not > I am filled with
During my four years of study, I could expand my knowledge on several subject areas: management, economics, computer science and mathematics. In my economics classes where students found many difficulties, I could further realize my great passion towards economics which enhanced my dream for graduate studies. During the first year I gained knowledge on introductory microeconomics and macroeconomics that offered me a solid foundation. During the second and third years I could explore advanced topics in economics through intermediate microeconomics, intermediate macroeconomics and econometrics. I am also enriched with the knowledge on business statistics, human resource management, business accounting, cost and management accounting, operations management, project management, strategic management, international marketing, entrepreneurship, business law, programming languages and artificial neural networks. I further believe that I am filled with the mathematical background needed for higher studies in economics. I followed courses on probability and statistics, calculus and linear algebra, mathematical analysis, real analysis. And I have the computing knowledge needed for statistical analysis.
to be continued
BTW - did you study in English at Peradeniya?
Student or Learner