Sorry for not checking store stock for you (you can do this from their website). I wasn't sure which store was closest to you. FYI, the Duluth store (address below) has an Open Box MSI A75IA-E53 for $50.96. I assume that's still eligible for the $40 combo discount which would bring your total for the mobo down to $10.96. Being that you're buying it from a brick-and-mortar store that's (assumedly) not too far away, I personally wouldn't have any problem buying an open box mobo. But it's up to you.
Microcenter Greater Atlanta/Duluth
2340 Pleasant Hill Road
Duluth, GA 30096
PS. Make sure to get the $40 combo discount with whichever FM2/FM2+ mobo you end up getting. You did buy a processor from them, not your fault you let them sell you an incompatible mobo.
PPS: You can call and have a mobo put on hold for you. I believe they can hold for 2 days(?)
Main: i5-3570K, ASRock Z77 Pro4-M, Asus GTX660 TOP, 500GB Crucial BX100, 2 TB Samsung EcoGreen F4, 16GB 1600MHz G.Skill @1.25V, EVGA 550-G2, Silverstone PS07B
HTPC: A8-5600K, MSI FM2-A75IA-E53, 4TB Seagate SSHD, 8GB 1866MHz G.Skill, Crosley D-25 Case Mod