I used to feel like this. I still get really nervous sometimes but it's way better than it was, and I have been told that I'm actually quite good at it.
I think preparation is the key - practice, practice, practice! If you're going to worry all week anyway, set aside some time to ensure that you know your material really, really well. Also, it's important to practise out loud, don't just do it in your head.
Also, remember that other people won't know how terrified you are inside. You might feel that it's obvious, but they probably won't pick up on it. And even if you do show some nerves, most people will be sympathetic to this. Fear of public speaking is very, very common, so most of your audience will fall into one of three categories: a) they used to find public speaking scary but have managed to overcome the fear and will be cheering you on to do the same; b) they still find public speaking scary and totally get how you feel; or c) there is no sodding way that they would be willing to get up and speak in front of anybody so they really admire you for getting up there and having a go!
Next, remember that it's just talking. It isn't a performance, you don't have to stick to a script. As long as you know what your main points are, you'll be fine. If you stumble over a word or two, don't worry - nobody will even notice.
Finally, don't forget to make eye contact with your audience and smile - it will make you and them feel more relaxed.
You'll be fine, good luck!