If a pixel of your LCD screen is black and it can't change color then this is a dead pixel. If a pixel is stuck in any other color other than black then this is a stuck pixel.
Usually you'll have about 1-2 pixel stuck or dead and will remain limited to those pixels, and will not get any worse.
There is only one way to repair the stuck pixels by using a color blinking video.Unfortuanly 3DS doesn't read any video files from the SD card with the current firmware nor plays Youtube videos.
Here is a color blinking video on youtube
So right now just play for a week and if the problem remaing then return it to Nintendo as 3DS does carry a one-year warranty.
Hope that helps. Please post your comments or tips about dead or stuck pixels
Thanks for the head up. I have now such problem at the moment with my 3DS but who know what might happen.