Where did you purchase it?
Viper Booq case which I was using for my rMBP still fits, albeit slightly snug but I love this case, hasn't shown any wear and tear in 18 months.
http://www.booqbags.com/us/sleeves/viper-sleeve/VSL13-BLK
I've got a basic sleeve for my 13" MBA and I carry that in a Colcasac "Jack Bauer" messenger bag.
I'm using this one for my 11" MBA.
http://www.amazon.com/Case-Logic-LA...747&sr=8-2&keywords=macbook+air+carrying+case
Lou
I use this one too and recommend it. It's inexpensive, sturdy (thick padding), and fits my 13" well.
I prefer the Viper hard case from Booq
http://www.booqbags.com/us/sleeves/viper-hardcase
I can carry the MBA, charger, cables, external hard drve, and even the DVD drive all in one sleeve.