i was the asshole sister

ok so my sis is like 10 years younger than me and we never really got along much growing up but she always wanted to be close. i mean, it's nice that she cares and all, but honestly she just gives me a headache with her constant need for validation and attention. one day, shes talking about this big thing coming up at school and asking me to help her with some stuff but seriously, i had so much going on already. anyway, i got annoyed and just said no like i dont have time for this right now. she looked super hurt and left my room crying. later that night, when i thought about it, i felt bad a bit but also was like why does everything always come back to me? i mean i try sometimes but it feels like the more i give her, the more shes gonna keep asking for. im not sure what to do anymore cause on one hand, its my sister and i shouldnt be so harsh but on the other hand, maybe i deserve a break too. am i just an asshole? do any of you have sisters or brothers that drain your energy like this sometimes?