I'd ask the vendor to refund your purchase price--or go to eBay or PayPal if the vendor won't cooperate.
Out of curiosity, what brand is the SD card? Here on the forums, the Class 4 Sandisk cards get the best reviews. Also, besides Gingerbread and B&N stock, what's the third OS offered by the card you have that doesn't work?
I wonder if switching your choice to a 16GB card might be advisable.
Although I've never bought from them (and have no connection to them), the n2a seller appears highly regarded and has great support to its users for CM7 Android.