AITAH for not wanting to spring on my moms last minute plans

AITAH? I (21 F) have lived with my fiancé (20 M) for alittle over 8 months now. I just left a really abusive workplace and have came to work for my mom (basic housecleaning and helping to take care of my grandmother bc she broke her ankle and is still in recovery). I normally work M-F 10-3 and that’s been plenty of help to give me steady income and help with her appointments. My fiancé works out of state M-F and we only get the weekends to see each other.

all of a sudden, my mom has a vacation planned and expects me to drive her to the airport Thursday and come on Saturday and clean the house then go Sunday to get her from the airport but without any compensation. (gas money or extra day pay) My budget is very tight and she didn’t tell me till today and now fully expects me to drop everything and be here. I have 2 sisters (18 and 16) that i said could at least do everything on Saturday and that would keep me from having to run extra trips 3 days. she won’t swing for that idea and says we talked about it months ago and I can’t back out of it now.

My fiancé and I have made plans already, my mom has been aware that the weekend is the only time i get to see him and spend time with him. I talked to him about it and of course he’s devastated because it’s hard being away and having so few days to do anything but told me to do what i think was best.

i’m being guilt tripped by my mom, my grandmother says she could make food and everything by herself. but i’m at a loss and idk what to think.

So would I be the AH if i blew off my mom and just kept my plans with my fiancé?