When I make a video I always SAVE it as I go along. When all the files I want for my Project are in the Media Bin I SAVE the it and give it a name. Then I put all the pictures into the Timeline in the order I want them. Then Save with the Save As... and add a 2 to the file name. Then put in all the Transitions I want and Save As... with a 3 added to the file name. Do the Pan & Zoom, do the Save As... and give it a 4. Add the music, and that's a 5.
Then if things go wrong you can always go back to a previous SAVE and do it again from there.
I play a keyboard and do the same when setting up REGISTRATIONS for a song. Habit, really.