RL_Dane, 5 days ago to ADHD

I've got an odd graphical problem and I need the advice of some #GIMP experts.

I use this image as my wallpaper, and I absolutely love it:
https://unsplash.com/photos/purple-and-black-pyramid-wallpaper-k1bO_VTiZSs

BUT when I use i3lock/swaylock, it's off-center which is frustrating in a very #ADHD way (see screenshot)

How would I go about cropping the image to make it centered? I mean, so that the little circular login indicator thingie is centered right on the innermost triangle?