It's okay to write terrible stuff. Anything you write will make you at least a little bit better through experience, truly. But, you should aim and strive for better writing, while not being discouraged. If your goal is to get better, of course.
If you write something terrible, it's a learning experience. Edit it and polish it as much as you can, and write something new taking what you learned from that into it. No matter how good you get at writing, this can still happen to you. Don't take it so hard!
I thought all I needed to do was write a worst novel than 
