High school is always considered as the most cherished period of one’s life. As a Senior 3 student, it won’t be long before I graduate. Now, I have much to share with my fellow students.
Firstly, I would like to show my appreciation of help from those standing by me all the way, teachers, parents and friends included. Without their help and advice, my life would be different. Secondly, it's high time to say sorry to classmates whom I hurt or misunderstood. Communication and smiles act as bridges to friendship. Above all, I've made up my mind to make every effort to study, for I believe hard work is the key to success. Just as the old saying goes, "No pains, no gains."?
　　Finally I hope that all the younger fellows can make full use of time, because time and tide wait for no men. soa natural?

"High school is always considered as one of the most cherished periods in one’s life. As a Senior 3 student, it won’t be long before I graduate. Now, I have much to share with my fellow students.
Firstly, I would like to show my appreciation for the help from those who stood by me all the way, teachers, parents and friends included. Without their help and advice, my life would be different. Secondly, it's high time to say sorry to classmates whom I have hurt or misunderstood. Communication and smiles act as bridges to friendship. Above all, I've made up my mind to make every effort to study, for I believe hard work is the key to success. Just as the old saying goes, "No pain, no gain."?
　　Finally, I hope that all the younger fellows can make full use of their time, because time, and the tide, waits for no man."

This DOES sound very natural and really only needs small changes with the idioms, which I've made above. You should be very proud of your incredible English proficiency and good luck in your travels after high school!