Sometimes it does take a few times to get a story through - I posted about it on here about my third story, I submitted that in total 5 times. The fifth time was going to be the last as I'd just about lost the will to live at that point, I usually get a story back once or twice then it gets posted. Luckily, it got posted. But getting the story back that many times meant that it was reread and edited each time and I added things to it. It was a much better story than it started out.
I must have learned something because my last story was posted first time within the time given, can't remember how long it is (three days?), and then I was nervous in case I hadn't checked it through properly.
Also when its been rejected, they usually tell you why. Then you need to go over your story with a fine tooth comb and check, then check again.
If you think your story is worth it, then resubmit. Don't lose faith in yourself.