I'm assuming Google Docs? I download it as a Word *.docx file, then upload that to Lit. Haven't had any issues with formatting, but I don't do a lot of tricky things.
Or you can copy/paste into the story text box, but I think you lose the formating.
Copy/paste your story onto the text. But you've got to double check and skim down after pasting to make sure all the lines are properly spaced. Sometimes when you paste, there might be additional lines/spaces in between paragraphs. Or, the paragraphs could be lumped together. So double check for that before submitting.