Honestly it is impossible for you not to feel nervous but you can prevent it from turning into panic. Well practice your piece while looking at a mirror first. Then record it and show to your family. when it is about time to declare it on class just think they are your bro/sis just messing with you :D also it would help if you eat,inhale exhale 10x and shake yourself before you recite
Practice, in front of family and friends, make sure you know it well, and can say it perfectly each time. Be confident that you can do it, and realize it is only a poem, and they are just people, like you. This is just one day in your life, and you can do it. Go get'm. Good luck.
Learn how to speak good English. THAT might help