Seems your white background wasn't completely white. it needs to be ffffff to be properly white.
You can rectify this if you follow these steps
Upload your finished image into gimp. Then with the color picker tool choose the 'pink' area. This color should now go into your active foreground or background color. Bring up the color to alpha tool and the color you want is NOT white. But the color that is in your active colors now (Usually black & white) Click on the color picker in the dialog that comes up (which may be twice). Once you color has changed to your active color then press ok.
This will make that area transparent. Put another white layer on it and put it to the bottom then it will be all white in the background
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