You need to do an average of 12-20 before you make permanent gains. The first ones are by far the most difficult and it is dangerous to stop once you have started.
Next time take a large dose of any magnesium you can get your hands on.
You are better off doing zero flushes than just one. But you are generally much better doing 20 than both zero or one.
Some people have a terrible time with it and wind up in the hospital but those people are rare. Still, you rolls the the dice you takes your chances.