Ah, I believe I may be of some assistance. You are experiencing what most would call "Writer's Block" which is actually just the fear of looking bad in front of the people who would read your works. You and everyone else has that little nagging voice that I would like to call the "Inner Critic" and the main problem here is that the things that are being self-critiqued do not even fully exist yet and are not actually formed.
That is to say, which is also the obvious conclusion, you doubt yourself too much.
So might I propose a question?
"If it doesn't exist yet, how can you know if it is good or bad?"
Keeping the same logic, I must advise you three things:
Grant yourself permission to look bad. At least if only during the drafting phases. Tell your inner critic that you will let it go crazy and critique all it wants but only during the editing phases. Essentially solving the problem of it critiquing your imagination.
Self Motivate. I have a trick where I grant myself instant and lasting motivation by way of listening to Anime Music or Inspirational Music. The truth is Writing is not for just those who have talent. Usually and more often than not, writers spend years upon years honing their craft and the Art of the Word. Thankfully writing is a Skill, and that means it can be trained. Practice doesn't make perfect, I only see imperfection strung together in a myriad of wonderful ways when I read any book.
That is my current motivational song. Make sure to right click the video and click "Loop" it is worth it.
3. Don't think, just do. Your problem lies in the fact that you are thinking about writing a story. However if you sit and think for any length of time, you'll have wasted that time better spent actually writing.
Take it as you will, I'm just some random stranger on the internet, but this random stranger's dream is to become the World's Greatest Writer. I couldn't let Writer's Block slow me down, and neither should you or anyone else for that matter.
That is all.