Jana, although I don't think the ship will be overrun by college kids, March does tend to have a lot of college students who are on spring break aboard. But I'm sure there will be other non-collegiates onboard as well. There will also be a lot of families and young marrieds. Three night cruises on Carnival at any time of year are usually....lively.
You may want to also look at a 3-night cruise on Royal Caribbean, which attracts a slightly more sedate crowd, or a 4-night cruise on Celebrity.