We all have those days when the fraud police just won't shut up.
"You did this bad! And you did that bad! And no one will read your book! And you're an impostor! And everyone will find out! And you might as well quit writing altogether!!"
Every day of your life you improve your writing—even when you don't write—your mind is always working, always growing. You can't stop it. You're a writer.
SO DON'T BEAT YOURSELF UP.
Tell the fraud police to go fuck itself. Take a day off. Do something nice for yourself. Treat your brain and body with respect. Sniff the flowers. Feel good. Sleep. And the next day will be better. Promise.