Feel like I'm being used but don't wanna let my parents down?

I start community college in a few weeks and missed my recent semester cause since I was in high school I cared for my little brother while my parents worked. now mind you that at the time that I did I had recently gotten out of a mental hospital so I was free all day since I was getting homeschooled where a teacher would come over and do work with me. I was 16 then but when I did go back to school I didnt have to take on that responsibility and it was refreshing because I struggled with it,I was going through a lot and I had to take on basically having a child.I graduated and my plans for college were to do community.everything was fine until I decided that I wanted to do AM classes but my parents were expecting me to babysit my brother again..we had this huge disagreement and I was left with no choice but to miss my semester cause I had no way to get to school,they refused to help me.They agreed that they wouldn't put me through this again that whole deal with who would watch him would be taken care of. a few days ago they asked me how I scheduled I scheduled my classes,I said im doing mornings so I have time for a sport in the afternoons and all hell broke loose they starting saying I can't do that dont i love mybrother I have to watch him that thats why im getting a car and it just really put me down because ive been watching him for months now, no human contact whatsoever.I have been planning for months on what I'll be doing during my day,what should I do? im 18