The First thing to do is to make sure that everytime you do anything in your checkpoint, that it says all changes saved. If it does not and you exit out, then it will not save.
However, it is not the end of the world if that happens. You can press the little clock with the circle being a backward refresh button, and that will take you to the edit history. There you can look at all of your previous versions and choose the one that either has all of your work, or most of it if you exited without saving.
I hope this is helpful. 🙂