AITA: heater conflict, mom yells at me to shut the fuck up

I’m 15. There are three heaters in the house, but one went missing and the other is always with my parents. The only heater me and my sister can use is the one we rotate. I had it for awhile time at first, more than four days, when nobody else wanted it. It was like it was sitting in a closet. I was the only one that was cold during that time. Then my sister asked for it, and even though she’s in a loft bed with multiple blankets and I only have one, I let her take for four days, because who cares.

After those four days, she let me take it back. I had it for about a day and a half, Then she took it again, after that day and a half. That was the only time we both wanted it, I was using it when nobody did. I was fine giving her it for four days before, but taking it back after I barely had any time when we both wanted it felt extremely unfair. I explained this to my parents, and said I’m fine with sharing. They told me I “owe” her time (different words, but owe sums it up) as their reasoning on why she gets to take it again, when I already let her have it before. Also, my dad sometimes took it into his office when I was using it, since his office is right next to my room and even if it’s not super cold, it still feels better. Point is, I wasn’t hogging it every hour on the days I had it.

Then, my mom said “life isn’t fair,” which on its own was not a big deal. I replied, “if life isn’t fair, then why can’t I use yours? You never share yours, it’s always in your guys room.” (I said it that way because her comment sounded like an excuse to make the conversation end quick, even though I had been using fairly) She said she was the one who bought all three heaters and that one disappeared. I said, “Its not your money it’s dads, and I didn’t have anything to do with the lost heater, so why does it matter if you bought them?” not because I care who paid, but because she is a shitty person and my mom doesn’t even have a job, so I didn’t see the point she was making.

(explaining all the reasons why she’s shitty is a whole different thing, I explain a small portion near the end)

She immediately yelled, “SHUT THE FUCK UP.” I didn’t really get mad back. I just asked why she said that, she just went quiet.

In the end, I did not get the heater. I was angry and my heart was pounding. And because of things she did when I was I think around four to nine years old, like locking me in my room and sitting in front of my door for an entire day with my sister having to wait for her to fall asleep so she could sneak around into a different room and unlock a different way out, I don’t have much respect left for her. When I was leaving I said, “fuck you too.” I only regret it because my dad now has to deal with the fallout.

Am I the asshole?

(Small vent) man, my life feels like a fucking cartoon. Shit that makes zero sense occurs, and then resets after a few days like nothing happened, whatever the fuck that may be.