It's one of those things you have to feel out for yourself. Each time you try it, listen to your body, and you'll know what to do. Perhaps you weren't ready quite yet.
Try again when you feel the time is right. You will remember how disappointed you felt by giving in, and it will be easier to continue on.
If you can't do the salt water flush, then make sure you drink lots of laxative tea. As long as you're moving your bowels once a day.
Try the salt water again in the future, and you will eventually be able to do it. I drink it warm and pretend it's soup.
Just remember, the first fast is the most difficult as you are releasing tons of toxins.
good luck