How bad is it? Do you see it when you're using it or only with the test? I ask because if you need the computer now, I would wait until you have a few days free to get it repaired.
If you return it, you run the lottery to get one with a Samsung screen. FACT. You'll waste more time if you get an LG one again.
If you wait until it's actually visible under your typical use, go to the Apple store and they will replace the screen. The time it takes can be anywhere from the same day to about a week.