I seem to remember it took my girls a while to figure out the door too. A week is not a long time to get some cats happily using a flap. In fact, our Jessica is a bit incompetent when it comes to the flap. Ours is magnitised and when they put their face up to the flap it releases the catch. Jessica just doesn't get it. She uses her paws to batter at the flap until it opens. During the night, the noise of Jessica battering the flap can be enough to wake us up (and not much wakes me up during the night).

It's quite funny to watch her at the flap, because as she is battering away with her front paws the flap is swinging open because the magnet on her collar is so close, but she continues to batter away! Perhaps she just likes the noise. I'm sure she must be exhausted by the time she gets in the house.