I am sorry to tell you that you may have lost some of your progress. On mobile, save your progress by doing this...
IMPORTANT: To save a copy or version a file so you don't lose progress on the Mobile platform:
a. Start Sketch
b. Go to Gallery and start a new Sketch, It will ask you to save the file.
c. Go to the Gallery and start a new Sketch again and it will ask you to save the file.
d. Open the first Sketch and work on it.
e. Go to Gallery and start new sketch and choose the "Save as a Copy" option.
David Lau