First, commit your local changes! Then try this
You hit a bug in makecode. Do you remember what you were doing right before the bug happened?
In any case, no worries! You’re using GitHub which means all of your changes from your previous commits are saved. Open the GitHub button and click “History”. Then click one of the dates and click “restore”. This will take your project back in time to that date and restore whatever you had then
Also, this is a non-destructive thing so you can always go back to what you currently have if it doesn’t work out.