I had the same problem when I first had my sky3ds card but mine was just a case of it not fitting the slot properly.I ended up pulling off the sticker as it was a very tight fit into the n3ds's slot.Once I had removed the sticker the cart went into the slot easily and it finally started working.
Mine has no problem going in, besides that I can hear / feel the pins make contact (so it's not smooth). I've tried adding paper. The sticker is flush, so I don't think removing it will do anything.
