Occasionally, the two ends of the pearl loop get crossed where they connect to the metal. (see the picture on the left.) This is likely why your rosary isn't laying flat. If they are crossed, you can just gently wiggle the two ends away from each other until they become untangled. Watch the video below to see an example!
If you look and these are not overlapped, please send the necklace back to me so I can re-string it for you a little more loosely. I want you to be 100% happy with your rosary!