Is AUTHOR wrong in the post ? POST : (Mobile Formatting)

This happened awhile ago but I didn’t know this sub existed so I’m going to ask it now.

I am 16 and don’t have an siblings, when I was around 10 or 11 my cousin stayed with my family for awhile and basically became my stand in sibling and I still view him as more of a brother then a cousin. I currently still live at home and my cousin will visit once in awhile and because he’s in college and short on cash my mom always offers him a job to do that doesn’t necessarily need to be done but my mom could care less and offers to pay him for it.

Whenever this happens I always get roped into helping him but I also don’t get any of the cash. So I do 50% of the work and he gets around $70. The last time this happened my mom wanted him to clean our crawl space in the basement and of course he said yes.  I once again was asked to help but in (what I meant to be) a lighthearted and joking manner said no and something like “can I get $10?” Both of them laughed and my mom said no. I said I wasn’t feeling like helping and my mom said ok (it didn’t start and argument or anything they both said it was fine).

Immediately after my cousin left my mom told me I was acting rude and entitled for not helping. I said that I didn’t mean to come across that way but I didn’t see why I should help when he is getting paid for the job. She yelled at me but wouldn’t give me an explanation as to why what I said was rude and entitled. Then she called me an asshole when I told her that I would actually like to know why I sounded like that so I don’t come across that way again. 
AITA?

Also, I posted this on r/ask when it happened and ended up deleting it because I was just getting downvoted and not getting any explanation. I am fully willing to except that I may have been the asshole here, but I really would like to understand why. 