Am i being selfish?

Okay so ever since I could remember I would always watch my neices and my sister would always pay me. Excitedly I would go home and tell my mom how much i made. When my sister is around she would always act proud of me. I remember that week she took me back over my sisters house and she asked me if she could use the $40 that i earned because she needed some gas and she didnt have any money. I said i need it and she constantly Basically harassEd me for it! Like i was trying to shut the door and she was like trying to open it back up begging for it so i just gave it to her. Keep in mind that i was like only 11 at the time. So when she got home she called me and said " i had 100 something dollars on the fireplace have you seen it?" I said wait, i thought you didnt have any money and she started yelling at me and hung up. She lied! That was the first time. Im currently 16 and its been going on since and im sick of it! I learned that i shouldnt tell her i have money cause all she wants to do is take it away and most of the time she doesnt even need it! It pisses me off. Im staying with my sister because she needed a babysitter for the summer and paying me 80$ a week. I used to go back to my moms house on the weekend she would ask for money like usual but this weekend i had enough. She suggested that we ate tacos and i was like yeah sure i guess. So we was at the cash register and she said " oh i meant to tell you that we need to pay half. So im going to need 20$ like wtf the shit for the tacos didnt even come up to $20 so why the fuck are you making me pay $ 20 as half! I lost it and said no. She made a whole complete scene in the grocery store. We was in the car and she was " you owe me $20 dont worry im gonna pay it back. It will really help me pay the attorney for your brother" like bullshit what is $20 going to do to help you pay the lawyer. And how do i owe you 20$ if you just said your gonna pay me back. All she talk is bullshit. And i refused to give it to her so she got mad at me and took me back over my sisters house saying she dont want to be bothered with me. I feel like i was being used all these years for my money. Oh their was this one time not to long ago she even pulled my from school to burrow 20$ for gas. I gave it to her and asked her can i leave school and take me to my sisters house. We got out to go in the gas station and she frickin pulled out 20$ worth of quarters to pay for gas. It was so embarrasing and confusing because i just gave her 20 just for the gas so i asked her why did she just do that. And her response was " So i can use the 20 for work to get lunch. Like wtf. I felt so used, am i being selfish or what?