@abrogard
Quote:
I still haven't progressed any further with it: that's how important it looms in my life.
Well, sometime you will want to fix it or prevent the same thing occurring again. When you ask a question of the "Why does this happen..." type. Give as much information as possible. A screenshot of the layers usually helps. If the graphic is flattened and a single image, your workflow becomes a guess.
Very obvious from your image the text layer has multiple lines and you just caught the top of the third line.
While editing you can enable
View -> Show All and that shows anything outside the canvas which gets lost when you export as a png or jpeg.
If you still have that and the text is still a text layer, just edit the text to remove the surplus line(s).
Otherwise if the text is flattened, erase or paint out. Easy in your case, it is a white background.
This a 1 minute animation of those possibilities.
https://i.imgur.com/rS5QOTA.mp4