Asma, without seeing the scribe it's hard to be completely sure and if you would like us to take a proper look please save your scribe it to your online cloud folder and send us it's name.
However on the information you gave me I would say that you probably have a fair few larger imported images in your scribe and are using effects or extreme zoom (outside the 10%-1000% range) on some of your camera positions. This causes a lot of memory usage and can cause the scribe to crash.
If that's the case then you need to make sure your scribe is set as close to 100% zoom as possible throughout the camera positions and this will reduce the memory usage and increase performance.
I am facing same problem. My zoom level is good and I do not want to save my work to cloud. App crashed again and again and I lost my work 3 times. Only 6 min video takes 2+ hour to get export even too that crashed.
When I change my scribe and save as .scribe file with me then it is saving my old work only not the changes. Really strange. What is the use of saving to .scribe file in that case if it is not saving my changes? This is a critical bug in app.