Let her settle in.

So against your excitement, you play it cool and let her be alone for a while. You stand around for an hour or so, then decide to watch some television. You barely pay any attention to what is on. You don't think to do anything else and eventually you doze off, spent from your excitement. You awaken a few hours later and head to your bathroom upstairs. Your new sister is occupying it.

"Hey, your bathroom is dowstairs, you know," you yell through the door.

"Sorry," she says as she opens the door suddenly after a minute, just as you went to pound on it with your palm. Your hand instead lands on her left breast, clad now in a big girlie night shirt that hangs to her ankles. She gasps and stares at your hand for a moment then goes to squeeze by you and gets her leg caught on your post-sleep wood. She 'eeps' and steadies herself by grabbing the protrusion. Realizing what she had grabbed she throws her hands up and falls to the floor. Her shirt slides up to her waist as she comes to a stop on her butt. She is fully revealed from the waist down but Cassie takes a moment to recover before she looks down. Her eyes go wide and she pulls her shirt down to her knees. She jumps up quickly and finishes, "I thought you were asleep." She then bolts to her room and slams the door.

Your cock is now hard from other things than sleep.