I am sorry to tell you that your progress/work maybe gone.
1. 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.
2. All sketches are local to the device. You need to back it up manually:
On Android, it's pretty easy, just copy the files from /Autodesk/SketchBook3 and copy it to your desktop computer. You can use the desktop version of SketchBook to complete our work (www.sketchbook.com/thankyou)
To re-import the file, you need to do this:
https://www.sketchbook.com/help/knowledge-base/back-files-settings/
See: How to import SketchBook files from an older version into the latest version SketchBook for Android
David Lau