I've tried saving as a .png but a GIMP message always pops up so I can't save it. Normally it says I have to format something.
If you're using the latest version of GIMP, try going File>> Export and then when you are naming the file, add .png at the end.
Example:
preset_3body.png
And then press Export.
Also if you get a message afterwards that asks you to export it as a flattened image (or something), make sure you press the Export button and then Load Defaults if another box appears after that
