You are using the best disks and the best program for this process. I like to burn DL at 4x, so you might try that speed if you were burning faster.
The layer break comes into play when you burn enough information on a DL disk that part of it needs to be burned to the second dye layer of the disk---which is the whole point of burning DL disks, putting more than will fit onto a single layer disk. So you cannot "avoid" layer breaks.
If this ISO is dvd-video, then you have to meet certain requirements when placing the layer break. It has to be on a cell boundary in the dvd-video and the cell must be on the edge of an ECC block.
ImgBurn will do all the hard work in selecting the correct position for the layer break. If one cannot be found, you'll get the "end of the world" error message. There is a workaround for this, but not within ImgBurn itself.
How many different layer breaks were you offered in ImgBurn? Sometimes there is only one appropriate spot, but normally you get several. I always select one that does not need a great deal of padding.