I first applied two coats of my current favourite black nail polish, Revlon Colorstay Longwear Nail Enamel in Stiletto, let it dry, then stamped on OPI DS Sapphire. To "solve" the narrow pattern issue, I first stamped the whole pattern to one side of my thumb nail, then I picked up half the pattern off the plate and butted it against the end of the previous stamped pattern (the to best of my ability). You can see that something went on there if you look closely, but at least there's no gaping black abyss on the edge of the nail. Sorry, I didn't get a photo of what it looks like.
My failed attempted at capturing the holo-ness.