Well, it depends on what site is. If the site is legit and they will pay you for your worth timing, then stay. Remember, not everyone will always fit to the site they are member of, the site won't adjust you. I would say, if you really want to stay in the site, you have to ask yourself all the reasons why. I cannot convince you because we have different reason.
For some reason, working online is not easy, some will require skills or talent or nothing at all. But then, if you feel not fit or good enough that's the time you can prove yourself that you can something you might not even know before. There is no harm in trying, in every success, there will always a failure.
I will always keep on trying, if it doesn't work then at least I did my best. And in the end, it's all up to you.