Haha yeah, I did mess up but it's ok because I know what the problem was. I was one frame under so now I know that for Thundurus and Landorus. I also plan on restarting my W2 because I want to play through again; I didn't really enjoy my first playthrough. Next time I'll get Tornadus-T right and I'll be able to get another Thundurus and Landorus :p
If you plan to do DR anytime soon, back up your Dream Radar save on your 3DS's SD card just in case you mess up. Problem is, though, even if you mess up you can only get one of each of the Therians per save, so you'd still have to restart your Pokemon game. But at least you won't have to restart your Dream Radar game.