Saving/Exporting problem?

[Ofnuts]

That's why there is "File>Export" and "File>Save". Formats such as PNG or JPG cannot hold all the information you need to continue working on the project. So you must routinely use "File>Save" to save your project as an XCF file (Gimp's native format that saves everything: layers, channels, paths...) and from time to time use "File>Export" to produce the required JPG/PNG/GIF....

Note that when you work on an image, if you try to quit Gimp without having used "File>Save", Gimp will tell you about unsaved changes, even if you used "File>Export".