Kozzie,
You can't expect to be perfect and natural if it's your first time teaching anything. Making mistakes is part of the process of learning to teach.
Memorizing your lesson plan word for word may have ''worked'' during your instructor course but won't go a long way in real life with real students.
Your first priority is to get comfortable by getting to know your student well: find out about their background, motivation to learn kiteboarding, prior training, share stories, crack jokes and have a laugh! Once the ice is broken it's all about setting simple goals and working on only one thing at the time. Remember you can't teach EVERYTHING, so select the most important information and keep it as simple and as FUN as possible. You WILL forget things once in a while, don't worry too much about it, move along and if it's important and you remember it later bring it back to the lesson, or wait till the second lesson. Avoid long boring monologues by regularly asking your student questions to get them as involved in the lesson as possible (e.g. what's a good spot for learning? What dangers do we have around us? What wind directions are unsafe? Etc.) The more you get your student to talk the more relaxed you will feel, the more fun you will both have and the more naturally your lesson will flow.
Also, try to make the theory more relevant and interesting by telling stories about things you've experienced, seen or heard in the past or simply by using live examples around you.
Write a new lesson plan (1-2 pages max) with a very simple structure and simple goals (what? How? When? Where?), and try to use as little words as possible. The rest will have to come naturally through conversation; don't write down what to say word for word and don't do monologues in front of the mirror, that's a trap!
Before you start working at a school, shadow more lessons and try to teach friends of friends (not close friends) to gain some experience and get comfortable. When you're in a school, discuss with fellow instructors, share successes and failures and gather tips and tricks from one other.
I hope this helps!
Christian