Yes you can save with the preview button. The next time you return to that forum you will see the box below. When you come back to the forum just click on Delete / Edit / Submit. To look at it again or continue before Submitting just Click on Edit it will be as you left it but no one else can see it until you click Submit. :) Hope that helps.
One time, I was almost done with an annotation, but they recommended that I save it since it was over a half an hour. They said, click preview and save, but the problem is that I did not know how to get to that preview button. This brings me to an important question. If I'm in the middle of an annotation here but can't finish it right away, how do I save it? What do I click on, and how do I get to the preview? This is important because I don't want to lose what I'm annotating.