Public speaking has to grow on you. The first public speech I made was terrible, but each one got better. The same thing will happen to you, so don't worry about it too much. Eventually I got to the point where I would take only an outline of what I wanted to discuss to the speech/lecture and just "winged" it. Those speeches are far more effective, and serve to encourage participation from the audience.
I did get tripped up one time when I had to give a persuasive speech in class at the University of Oklahoma. We were supposed to cover a topic we were familiar with, so naturally I decided to talk about skydiving, a sport I had never participated in. I skimmed a book on the subject, and the speech went well. I had the class in the palm of my hand. But, unbeknownst to me, my instructor was an accomplished skydiver. He asked several questions to which I bluffed my way through. After class, he took me aside and asked if I had ever skydived, to which I responded truthfully. He thought it was funny, but I still got a B on the speech.
I have since gone skydiving, and heartily recommend it.