Reneged on a negotiation -- New Job?

I think you should relax. You have a signed contract and the company is required to honor it. No company is going to risk a lawsuit over three days wages, so they probably just need a few days to do resolve the situation internally between HR department and the Provost.'s office. Give them a little time to work it out. I strongly suggest you don't make any comments in the office about the situation until you see how it resolves.