I managed to startle a whole bunch of MA students yesterday by telling them to write rubbish. It wasn't what they were expecting to hear. But it was in response to a question about writer's block, and getting over the fear of the blank page. 'I look at it,' the student said. 'And I just know I'm going to write rubbish. So I don't write anything at all.'
But the worst bit of rubbishy writing on the page is worth more than the most perfect bit of prose stuck in your head. Stuff on the page can be improved, developed, tweaked,given colour and life and energy and style. Stuff in your head is - well, stuff in your head. It can't be read by anyone.
Give yourself permission to write badly. Accept you'll have to re-write - and I don't think there can be any professional writer who doesn't consider re-writing as part of their process. It's what we all do.
An agent won't read your work with more interest because it appeared fully formed on the page. An editor won't clap their hands in delight because you wrote in a linear way. A reader couldn't care less if you didn't need to use the spellchecker. A tutor's heart will sink if you present work saying you haven't rewritten because it's perfect as it is.
All that anyone cares about is the finished product. How you get there is up to you. Write rubbish, if it gets you writing. That's all that matters.