Apparently they're canceling all of them.
http://kotaku.com/walmart-cancels-sn...itc-1797277387
“Unfortunately, due to a technical glitch, the Super Nintendo Classic Edition was mistakenly made available last Friday evening ahead of the official release date,” reads an email that Walmart just sent to those who pre-ordered a SNES Classic. “We, regrettably, will have to cancel this item on your order. We know that this is incredibly disappointing to you, and we’re truly sorry for this mistake.”
If you still have a Walmart pre-order that hasn’t been canceled, the wording of this email indicates that your SNES Classic is not long for this world, either.