All of your careful preparation and attention to design will be for naught if you cannot deliver the information within your time limit and in a compelling manner. This takes practice, a lot of practice. And not just repetition. As this quote my high school band director used to repeat, "Practice doesn't make perfect...perfect practice makes perfect." What this quote really refers to is something called deliberate practice, which is a process whereby you concentrate on those aspects that need work, not on mindless repetition of what you can already do well.
You may think that people who are excellent speakers are just naturals at it and don't practice...that they just get up and wing it. That is rarely true. Musicians don't perform without intensive practice beforehand, and neither should you. As you become more comfortable before an audience, the time you spend practicing may diminish somewhat, but you always need to ensure that you can deliver your information in a smooth, confident manner. Give yourself plenty of time to practice so that if you need to alter your presentation--cut out some slides, or modify some slides for better comprehension--you will be able to make changes and still have time to practice.
If possible, practice in front of other people and get feedback. If you've never spoken to an audience, it helps greatly to deliver your presentation to even a few other people. If possible, videotape yourself and then analyze your performance to see what needs to be improved. You will be surprised at some of the things you do that you may be totally unaware of, but which detract from the message you are trying to deliver. Practicing beforehand also gives you confidence that you can deliver the information effectively--and this will reduce nervousness.
A word of caution, however. Don't memorize your talk. That is asking for disaster. You may memorize the main points, but not exactly how to say them. You can also memorize your opening and closing statements, but again, be prepared to have trouble remembering exactly what you wanted to say. When you are under stress, standing in front of the audience, your brain will desert you just when you need it the most. So have some alternative, generic statements ready just in case.