A bit of context:
 Im 17, last year of high school, i live with my mother and sister. My father isnt really around, normally hes gone because of work.
 My sister is 13 and in the the last year of middle school.

 The chores in our house are separated between me and my sister. My mother doesn't really do much(cooks once every week or more) even tho she stays at home.
To be fair i cant say she does not work tho, but its somewhere in between, she does work but she has plenty of free time.

 I wash the dishes daily(takes me around 25-30 mins in good days),I go buy whatever is required(doesn't matter if I have to buy 1 or a list of things, takes me around 30 mins in the best days and can go to wasting half a day on really bad days) and i have to clean the bathroom on cleaning day.

 My sister has to cook(when there is no cooked food in the fridge), and by cooking i mean pasta or rarely sweets, and do the rest of the house on cleaning day.(the house takes around 2:30 if done properly and cooking takes 15 mins)
So realistically she does not do much most of the week, since she maybe cooks twice a week.

 So today like any other day(still in vacation tho) i wake up, wash the dishes ,do some homework, go buy food and around 8 pm i finish everything and go to my friends house(i do live very close to him).

 At 8:50 tho i get a call from my sister to come wash like 5 dishes cuz she wants to do pancakes. I say no because i already did my job today, and i tell her she does not need them(besides the pan), and that they wont ocuppy much space either. Plus why should i waste 15 mins to do what she could in 5?
That aside, she gets mad and tells me she wont make any for me.

 Around 10 pm i get a call from my mother to go buy some things necessary for the pancakes because she forgot to tell me earlier when i went the first time, at wich point i am forced to abide since they are necessary ingredients.

 In the end i do get 1 pancake, but its not the first time im asked at 10 pm to go buy some forgotten thing or to come wash some god forgotten dish(happens pretty often).

But i do have to be fair at least. My sister does do a lot for her age, but im not some stone golem, I wont compromise my free time(and we're talking about max 4h of free time) and happiness for unecessary things. Plus one philosophy I try my hardest to uphold is less effort for all, if can do something that aint my job with less effort than somebody else I will do it(if its NECESSARY). But i expect the same thing in return, otherwise I wont.

Tl;dr So to close this off, AITA for not wanting to come home to wash 5 dishes, when my sister could've washed them herself in less than half the time it would take me?