Setting boundaries with a parent that doesnt care?

I'm having an issue with my mom, every tike i try to set a boundary specifically aroynd watching my siblings she literally ignores it or gaslights me. Im 18 and i want to move out but ive been trying to get a job for 5 months and literally cannot get one. My mom goes out with her boyfriend pretty much every weekend and usually tells me she'll give me $20 but i have never once been paid (been baby sitting since maybe 10) and my siblings are BAD they have no respect for ne and my mom does nothing other than tell them calmly to be nice to me. Im loosing my mind and feel so used. I have tried a few different times to tell her i will not watch them anymore and she will come up with a plan to 'trick' my siblings into thinking she wont leave but she literally just walks out the door immediately and leaves or she'll manipulate me into feeling badly. Is there anyway to fix this? Or do i just need to stick it out a little longer?