Face your fears down.
Fight against your fears controlling you.
Don't bunk off school. Deliver the speech.
Open the speech with an attention grabber.
Don't read a speech out. Talk from the heart, as if you're talking to a friend, except louder so they can hear at the back. If you have time, learn about memory pegs for memorising lists (1 run 2 zoo 3 tree etc) and organise what you want to talk about into a memory peg list.
Focus on your audience. Don't focus on what you're feeling. Don't stay trapped in your head.
Aim to end the speech with a call to action, or a summary of the main message you want to put over in the speech.
Tell a story or one or more anecdotes in the speech that will illustrate the point you want to make. The attention grabber can be something from the story or an anecdote, such as a dramatic moment in the story. EG "Smack! (with you clapping your hands loudly) The pain was terrible..." as an attention grabber with you then telling the story about how you got into the accident.
Treat this speech as practise and learning for speeches you will make later in life.
Don't spend too long preparing this speech. You have all the other things going on in your life.
Put emotion into your speech. Don't talk like a robot.
Don't worry about grammatical mistakes and using the perfect words for everything. Don't worry if the odd swear word slips out.
As you speak you should find that the speed you speak at varies, depending on what you're talking about. Sometimes slower, sometimes quicker.
Accept that no speech is perfect. And that your speech won't be. Good enough is good enough. And if anyone doesn't like your good enough speech, that's tough titties on them. With bar on good enough being very low, because you're a school kid in year 11 that's never received professional public speech training.