One possible version:
Dear principal,
I am Li Hua, monitor of class 1, senior Grade 3. I am writing to report us students’ opinions on our PE classes being cancelled.
Facing the coming college entrance examination, we Grade 3 students all feel stressful. One of the effective means of reducing our pressure is taking exercise including having PE classes. That is why my classmates felt frustrated and helpless when hearing your decision. We believe taking exercise can keep us more healthy, more energetic to improve our grade. It can also strengthen our friendship and we can do less for more when learning. As the saying goes: All work and no play makes Jack dull boy. Considering all the above, we sincerely hope that you do not cancel our PE classes therefore. By the way, having one more PE class each week is welcome. Thank you!
Yours
Li Hua