Doesn't Saving Worlds

The minecraft Pe doesn't save

I builded a giant castle using 1 or 2 hours I wanted to put it into minecraft forums I was
very happy but when I quited to title it doesn't saved the things I builded

what happend step by step:
1.build
2.quit
3.every thing you worked hard and used time,used imanigation and your creation is gone for ever why?!(I hate useless)