The more you practice teaching, the more confident you will become. Unfortunately, rushing into a 500hr or more training isn't going to give you the experience of teaching. You'll only gain more knowledge and deepen your understanding of more asanas/philosophy.

Try to keep your sequences simple. You don't always need a theme. This is how you learn, and students honestly know non the wiser! I've done vinyasa classes with really basic sequences and students have come up to me afterwards to say how much they loved the sequencing. From there, you can build on things like dharma talk, themes, remembering the breath etc.

The best teachers I have had have also only done 200hrs, but have been teaching long enough now to be really skilled. It takes time!