I need to vent !

Tell me if I'm being irrational but I'm just really irritated and I've had a horrible day ! Anyways my moms car is messed up , but she started a new job this week . She needs me to take her and pick her up wed-Friday because her fiancé is going to be out of town . She's going to give me gas money but it's like 30 minutes away , I have a 11 month old , and I have to be at her house at 730 . And then back to pick her up at 3.  LO dosent usually get up until 945 , and then naps at 2 . This is going to throw off his schedule ! I really don't want to do this but idk how to tell her no , because it's my mom and she'd be there for me ! Ive been on the verge of tears all day , just feeling down bad now something else added to my frustration ???