Not sure, but I think you have inadvertently pressed the "s" key...this hides the stitches and leaves only an outline...try re-pressing the "s" key and the stitches should reappear...hiding the stitches when digitizing sometimes helps to see the shape and/or outline of the design you are digitizing...the "s" hides them on a toggle and repressing the "s" brings them back...let us know how you do!
When something like that happens use the undo-key/button/arrow before trying anything else. And as advised by sandyqueen: save often. I don't do it automatically, but save with different names - xxx-step1 and so on. Easy to go back to a former version if you decide to tackle it differently.
Hopefully you saved your design frequently. Go back to the last one saved. If not my software allows timed saving. I set it for every 10 minutes.
Save your work frequently while digitizing and you can go back to last save, not the beginning. Isn't learning fun.
SQ