Changed my schedule 3 days before I work it...

I'm a new nurse, just finished precepting and will begin my first solo night on Tuesday. When I asked last month about being able to still have the same schedule as my preceptor so that I could have a go to person, I was told that it was fine by the two nurse managers and the charge nurse who does the scheduling was aware of this. Our new schedule started yesterday (Sunday) and had not gotten past the "2nd Draft" stage because the charge nurse was gone for like 2 weeks... So I assumed I'd still work the same schedule that I put myself down for and made plans for this 5 day weekend I had coming up this Thurs-Mon. This morning I get a message from the charge nurse saying she has taken me off of this Wednesday and has put me on for Saturday because they were short... huh? How can she tell me 2 days before that she's changed the schedule (to a day when my preceptor can't work and this will leave me without my go to person for only my second day off precepting) when I know in our policy manual it says they are required to give us at least two weeks notice? I don't know what to do... I had made plans for this weekend already and I could really use the 5 days off in a row... I am coping badly enough now and was wanting to spend some time with my family to help keep my spirits up... I am so upset that this has been done, but I don't want to ruffle any feathers so soon... what should I do? I am so depressed as it is, I really was looking forward to this weekend... I need advice!