Sisters graduation

My little sister is graduating Monday, my mom just informed me today. I have a child with ASD and we have his speech, occupational, physical therapies that day and I’m working. I told my mom that and she isn’t responding. I know her she’s probably super mad at me. Even if I canceled everything, I still have to bring my 5 yr old to the ceremony as his dad is working. They run like 3hrs long, I can just see him acting up , me getting really stressed bc he’s being disruptive. I’m 6weeks pregnant and I don’t want to be putting to much on myself . I already feel like I’m doing too much. She’s having a graduation party which we will be attending. Am I a bad sister?