'The simplest things in life...' - The extracurricular part of common app

I need to cut this down by 42 characters.And if you could comment on grammar and anything else it'll be appreciated.

The simplest things in life could bring you the greatest of joys.
This I realized as I watched the faces of students light up with bright smiles as I informed them that the challenge 2020 initiative had decided to take up a project in their community school.

The challenge 2020 initiative is a non-profit team set up by students to reach out to our immediate community. As the secretary, I was very proud.

I had spent my last year of high school writing letters for sponsorships to individuals, of approval to the LGA, organizing fund raising events, raffle draws and internal competitions to raise money for the building project estimated at N10mil.

We had managed to raise N4mil. And get a volunteer architect to sketch up the plan for the building; 2 storeys, 6 classrooms, 3 toilets and a first aid room. It was to be the only cement structure in the complex.

As I stood there watching the students jubilate and make merry, I saw flashes of the years' event before my eyes and a feeling of full contentment flooded my soul.

Your second sentence is hard to follow. Instead try:
The simplest things in life could bring you the greatest of joys.
I realized this as I watched the faces of students light up when they learned the challenge 2020 initiactive decided to adopt/undertake (choose one) a project for their school.

OR
Watching the faces of students light up while I informed them the challenge 2020 initiactive decided to adopt/undertake (choose one) a project for their school, made me realize the simplest things in life could bring the greatest of joys.

As the secretary, I am very proud.

I spent my senior year of high school...

writing letters for sponsorships to individuals, of approval to the LGA, --what do you mean?

organizing fund raising events, raffle draws and internal competitions to raise money for the building... Instead try:

organizing events such as internal competitions and raffle draws to raise money for the building...

Your last sentence is great!

This is an excellent topic and it shows the characteristics of a good and involved student.

And get a volunteer architect to sketch up the plan for the building; 2 storeys, 6 classrooms, 3 toilets and a first aid room.this isn't a well structured sentence, you realy shouldn't start with "and"

Try to make i flow more, but the topic itself is EXCELLENT!