When I was at American, they dropped a lot, and Fordham, which I turned down (they offered me a small scholarship but DC was still a smidge cheaper) was skyrocketing up and it was upsetting as *fuck*. But a large part of why American dropped had to do with physical plant, as the school buildings sucked but the school was building a new space a mile away and of course the rankings didn't look at that and the building didn't open until the January after I graduated anyway.

Anyhow, what matters more than the ranking before you start is the ranking the year you graduate - and where it goes from there. So (a) can you still change school choices if you truly want to, and (b) maybe you should talk to the school on Monday or Tuesday to see what they are saying. Take it with a grain of salt but it isn't the be-all and end-all of it.