MadMonkey's right. Your RC didn't fail, but your awareness simply wasn't high enough to notice that having 6 fingers meant you were dreaming. If you do a lot of RCs in waking life, especially if you don't really take the time to question what's around you and whether you're dreaming, they'll carry over into your dreams without you being aware enough to notice them. You were very close to a lucid though, keep it up! Just work a bit more on your awareness.