Camping with family - The week before

An incident that happens the week before nick goes on a family camping trip

"Whoa, hey im kinda busy here!"
I shouted as my sister barged into my room, throwing my door open and getting an eyeful of my dick in my hand.
"Well christ, Nick, why didnt you have the door locked?!"
She shouted back, slamming my door back shut with a flustered look on her face. If i didnt know better i would swear i saw her throwing another glance down to get a second look.
"Oh yeah sure. You could have knocked as well you know."
"Yeah, yeah, whatever im sorry. I just wanted to talk about the camping trip next weekend. I guess just come to my room after you... finish."
Heathers muffled voice came through the wooden door, and then i heard her footsteps move down the hall.
'Finish, yeah good luck now. Kinda killed the mood.' I thought to myself.
I cant believe she just burst in here like that. I dont do that to her, who knows if shes in there changing, or hell, even what im doing right now.
All of a sudden a mental image of my little sister, naked in her bed, flashed through my mind. And it made my dick hard. I had never considered my sister to be attractive, but that one thought going through my head changed that opinion instantly.
I could see where she had developed a cute bubble butt and small, but perky breasts, going from a flat chest to maybe a b cup now. She wasnt a kid anymore, but a young lady who had just finished her freshman year.
The Heather in my minds eye played with herself, pinching her nipples and rubbing her clit furiously while i stroked my 7 inches. I had been close before my sister barged in, so it took no time at all before i shot my load on to my bedsheets, thinking of my little sisters jiggly ass being covered in my cum.
Taking a few minutes to soak in the shame of what i just did, i cleaned up my mess before walking down the hall to Heathers room. As i got closer i could hear a bit of shuffling inside, and thought 'I might as well give her a taste of her own medicine.'
Instead of knocking, i simply threw her door open, a perfect rendition of what she had done earlier, saying "hey sis, whats going on in here?"
Unfortunately i didnt get the view i was hoping for, as heather was at her desk organizing some shelves.
"Oh hey, Nick. Man, i didnt think youd finish that quickly. Or maybe you were hoping to see me changing for bed. Dont worry, i wont tell anyone." She giggled to herself.
"Oh yeah, hardy har har. I wouldnt try to peek at you, youre my sister, no matter how hot you are."
Heather heard my mistake.
"What was that? No matter how what? I didnt quite catch that."
"Ah shit. Fuck, uhh. What was it you wanted to talk about? Something about camping?"
"Just gonna sidestep that entirely, huh? Smart. Look, youre the one thats planned and packed everything. I was just wanting to ask if you think we'd have enough food if my friend Cassie joined us? I havent asked mom yet but i wanted to make sure wed have the supplies first."
I rolled my eyes at her, while celebrating internally. I would absoultely love it if Cassie came along. I might have thought of heather as an annoying runt until an hour ago, but cassie is another story.
Cassie is maybe a year older than Heather, and it shows. She started developing early, and at 15, she had a body professional pornstars would kill for. She had hit the genetic lottery, sporting at least E cup tits and an ass that would take both hands to grab a single cheek.
I was thrilled by the idea of her joining, but i couldnt let heather know that, so i put on my best poker face as i replied.
"Great, another brat coming along. Im just gonna go ahead and saaay, no, we dont have the supplies."
"Come on, Nick! You always over pack for stuff like this. You literally brought like 3 days worth of supplies to go float a river. Plus, wouldnt it be better having 2 hot girls in swimsuits to look at?"
She had a shit eating grin plastered on her face as she tacked on that last sentence, which broke my poker face.
"What do you, uh i meah *ahem* im sure i can work something out with what we have."

This is the first part of my first story with anything sexual. Let me know what you think