I thought my purple Yoobao was off center too until I pushed the iPad all the way back into the case. As for the accidental activating of the wake/sleep feature, my Yoobao case stays closed even in my purse.
Everything else in the back gets misaligned when I do that on my brown one. The camera hole doesn't get covered but it's way off centered. It's also only a temporary fix as the iPad slides back to its natural position of being slightly to the left.
My brown one activates sleep/wake everytime I pick it up. How do you know it's not constantly switching on and off in your purse as the nose isn't very loud.