Unfortunately I was unable to update Luma, but I was trying to open it via the executable in the 3DS menu.Just download the latest version on your PC or Mobile device, and put "boot.firm" on the SD root, replacing the existing file.
I opened it by holding select before the console boots and then I managed to select the option '' Enable loading external FIRMs and modules '' I checked and pressed Start to return to the 3DS Menu.
It's running on Widescreen now, but the image looks... should it look stretched like that on the 3DS?