No problem. If you make any mistakes in your visitor messages and want to fix them, in the right corner of your VMs, there's a link to edit them. This way, you can fix your VMs without having to write a new one.
When you're ready to post to Fanfiction & Writing, you start a new thread and copy/paste your story into the post box. Make sure your story/chapter is complete and fits the rules of the section in every way, and you'll be all set.