Job, do I quit!?!

I recently got hired at a bar and the owner told me I would be full time with the current bartender and I agreed with that, but a week later the other bartender/ manager hired her mom and brother, and the bar is open Thursday-Saturday but now she put me only working Thursdays and her mom and brother get the weekend the problem is Thursday are pretty empty and mostly cleaning I asked if we could rotate so I can get the weekends as well and she said we'll they are training for the next month like wouldn't it make more sense to train on days that are slower?? and you will get Thursdays and be on call if we need you? Like I just started as well and I feel like their is favoritism I don't think it's fair i tried talking to her and I know she's closes to the owners, should I just quit? This isn't what I was told when I was given the job, do I talk to the owner would it even make a difference I know they are friends