Painted and saved my original image in error

[Ofnuts]

The Erase tool only acts on one layer at a time so I don't really understand "f I use the eraser, it removes all the image layers". Since you duplicated the layer, with some luck you didn't paint on the initial layer. Make all layers invisible except the bottom one in the Layers list (click the eye icon) and see if the paint strokes are still visible.

Also, in Gimp you "save" your image to XCF, and "export" to other formats. Did you export over the initial image? If not you still have the unchanged image.