I would still contact them (reseller) and inform them of the mixup, provide them with photo evidence of the mismatch so they have it on record. This way, if you have any issues and need to claim on warranty or RMA, you won't have difficulties due to the SN mixup. This is not an uncommon issue. A user buys 5 boards, sends one back in the wrong box or their tech department is testing 10 returns and puts a good one in the wrong box etc. Typically it is an issue most retailers will try to avoid but it happens more than many people think.

Always play on the side of caution with things like this. You need to inform the retail outlet that your serial numbers don't match. The last thing you want is to need warranty and have it denied because they accuse you of board swapping. Don't panic though, it is unlikely they will give you any trouble. If the board has ever been returned, that will be on record and they will know what happened. 

Good luck, let us know how the build goes for you 

Well the board was sold as new so I'm thinking the mix up occurred when they were flashing the BIOS to support Ryzen APU's.  It was not marked as a refurb board when sold and by law it has to be if it was a return sent back to the retailer.

There are numerous reasons a new board can be unboxed and repackaged and still sold as new. Boards are only marked as a refurb if they have been out to a client and returned. In house testing, product inspection, packaging replacement due to physical damage to the packaging but not the contents. Should or shouldn't happen, they do. Marking anything "refurb" means profit lost and every retailer does everything possible to avoid that.

Regardless, my advice still holds. If the serial number does not match, report it to your retailer. It could cause you issues down the road even if the board works flawlessly now. At least this way they will have the board's actual serial number associated with your purchase for warranty purposes later.