Now my tummy is starting to get nervous

I found out about a week ago that my summer job will not be full time as promised. Last summer when I was hired the plan was to job share with another student who had one year of school left. They hired me because they wanted someone with several years left in their degree so that I could continue the same research summer to summer. The plan for this year was the work to be full time (as told to me first when I got the job last year and reiterated up until last month). I had a class with the professor this semester who promised me the full time work and he told me as I was handing in my final exam. He said he wanted to give some work to the student who was graduating and I could just ask the math department for part time work like I did last year. WHAATTT! I was offered 3 jobs over the course of this last semester that I would have loved to have. I turned them down because I had already committed to working for this professor. There was another job that I would have loved to have that I could have applied for. The start date for all of these is tomorrow and they've all been filled. I have no idea what I am going to do.