Hi , the 2 button key you have for your sportcross is the correct original key ,the sportcross was not issued with a 3 button key as there is no key access for the rear hatch which is operated by the central system ,the key you have is probably a master if it fits all locks as you describe ;
Dave
Don't pay Lexus for a master key!!!
Join the Facebook IS200 group, I'm an admin of it. Another admin "the original Stoney" has master keys for sale and will include this guide http://www.lexusownersclub.co.uk/forum/topic/48876-need-a-new-key-you-need-to-read-this/?fromsearch=1
That he wrote a few years ago when he was a member here, he is no longer active on this forum.