I bought a desktop from newegg.com iBUYPOWER Desktop PC ARC NE621FX-1 AMD FX-Series FX-6300 (3.50GHz) 8GB DDR3 500GB HDD Windows 8.1 64Bit - Newegg.com
"Eligible for free game offer, please go here after purchase" and i redeemed it but I redeemed Tomb Raider to steam because I thought Dirt rally was the first game in the series. ( but dirt showdown is)
Technically Colin Mcrae Rally was the first, then after his death Dirt - Dirt 3, then Showdown, then Dirt Rally. But this is just me being a rally fan picking holes. Sorry.
Sadly once you have entered the numbers into Steam, that's it. Steam are fairly strict about things like this.
I have just noticed also this post was made mid last year but there's and answer anyway.