Reply: Sibling Sex Guilt

So, once and only, once when I was fifteen and horny as hell, I talked and coerced my chubby ten year old sister into looking at online porn with me on my laptop while our parents were at a wedding.
Eventually it became every obvious that the vids we were watching, the vids I let her click on, were definitely getting to the both of us. 
She was showing interest after her initial "Eeew" reaction. it took her a while but she eventually asked about my penis and I quickly introduced it, bringing it all out through my zipper. 
I engaged her in a detailed conversation about masturbation, answering her all her questions as well as showing her vids and demonstrating. I guided her hand and she gripped it gently while wearing a shit eating grin on her face. 
I asked about her masturbating and the pink flush of her face answered my question before she said a word. She just nodded her head and admitted to humping her pillow. 
I slowly reached over and gently pressed the back of my hand against her vagina over her sweatpants. She parted her thighs slightly and moved her hips forward to meet my hand without making eye contact with me. 
Emboldened, I asked for sex. She declined, fearing possibly making a baby in her. She was too young, I was not about to explain it all, I suppressed my instinct to giggle. So I asked about jumping against her butt crack. She immediately agreed and rolled on me tummy. 
We both lowered the back of her sweatpants enough to expose her chubby bubble butt that I had already jerked off thinking about a couple of times. I climbed awkwardly on her and while keeping my body weight off of her with my hands on either side of her shoulders, I slid my erection along her butt cheek's cleft.
My erection slid freely, leaving a small trail of precum. I pressed in more and it buried itself between her butt cheeks. She moved her hips in a humping motion as I humped against her the soft skin of her firm butt cheeks. 
More precum lubricated the path. I adjusted my erection with my hand and felt the tip of it find the warm opening to her anus. I rubbed it back and forth, lubing it with precum. Then slipped the tip into her.
She immediately got up on her elbows and acknowledged it was going in. My shaft followed gently into the warm and firm grip of my little sister's anus. 
Still on her elbows she dropped her head down as she said my name and cursed but actually tolerated my penetration into her surprisingly well. I humped gently and shallow as my penis was only about only 3/4 in her. Then I just shot my squirt into her with a grunt. I came so fast.
I immediately became soft. She clinched her sphincter and I slipped almost out. As I got off of her she passed a little gas and we both giggled a bit, but then there was a shift. 
She seemed very annoyed that I did not last anywhere near as long as in any of the videos. She questioned if , she got dressed and stormed off from my room. She went to the bathroom a while then locked herself in her room.
Our parents arrived about an hour later. I was so scared. My sister never told on me.
It's like it never ever happened but we are not close at all. It's like there is a wall. It's diplomatic but not really warm. It's polite but distant. I feel terrible about having done what I did to her.