No need to be anxious. Take your time, read the articles in the Help & Info section, and feel free to ask for help if you need it. There are plenty of writers here to give advice and critique, if that's what you need. Write the best that you can, proofread your work (ask someone if you don't feel confident doing so yourself), and have fun with it. Glory or bust, it won't matter if you take it as an opportunity to grow.
As long as it's not a half-assed story, most of the people are more than willing to help. So write what you want to write and enjoy!