Games : Forgot to Do System Transfer on old 3DS XL, can't login to old NNID

I just picked up the New 3DS XL and never knew about the system transfer until now. I did the 3DS exchange for $100 with GameStop without knowing about it. The GameStop employee didn't inform me either. I have the old SD card from the old system.

Is there any way to unlink the NNID from my old 3DS so I can login into my new 3DS?

Is there any way to salvage the save data from the old 3DS with the SD card I have to put it on the new 3DS?