According to your layers panel. The top layer is a text layer ans the second layer is a raster layer. A raster layer once the file has been closed, can not be undone. It would need to be recreated. If for some reason you left the file open, then it maybe possible to undo it, as it would show in the history stack. But by default that stack is set to 20 states, so doing more than 20 things would push it off the stack.
I think you are going to have to bite the bullet and redo that layer.