metal is the #1 culprit of getting errors with the compass. I had a situation where I was at a park and placed the phantom on what appeared to be a concrete slab bench. It had metal tabs to keep it in place so people can vandalize it (basically metal restraining tabs). each tabs were about 3 inches wide and about an inch thick. this was enough to give me compass error when I put my phantom on the bench (even though the compass was a good couple of inches away from the metal tabs). I took it off the "bench" onto the ground and that cleared the problem i was having with the compass. I won't be surprised if watches or rings will cause the same errors.
If no metallic items are around and you are still having errors, try the above video trying to reset the compass. if it continues, i would go ahead and contact the dealer since it may be a lemon.