Am i being selfish?

I’m 17 and take care of my 11 month old baby bro all the time. My stepfather doesn’t believe n changing diapers so I have to do it. I recently got back in contact with my dad and his family after 5 years of no communication and they want to see me tmr at this party thing they planned. Today, my mom got into a car accident and got stitches on her forehead. She can’t breastfeed till tmr but other then tht she can still move around take showers talk etc... i cancelled with my dad tmr and he understood. My mom got mad bc she wanted me to go tmr and not to long just for 2 hours and i secretly wanna go to but ik they need help around the house. But since we been home my mom has been the exact same just sleeping and instead of my stepdad helping me with the baby he’s sleeping with my mom. Then he gets hot really quickly and has the AC on at 64 and i get cold really quickly but the AC is blasted where the baby’s play room is and i asked him if we could switch for a little and he says no ur mom needs my help even tho he was gone for a few hours today and i took care of my mom just fine. She wants me to go just a for a few hrs and so does my dad and i kinda want to also. My stepdad is saying no and that bc he just doesn’t wanna take care of the baby bc my mom doesn’t need taken care of she’s making her own food and eveything still...idk. Just all summer (my last summer before college) I’ve been stuck at home watching my baby brother bc they don’t like baby sitters and tmr when i finally really get to leave this happens..and he has a 30 year old son who offered to help but he said no bc his son shouldn’t have to watch his brother...but I have to ?