I think it’s because I ducked up my math (calculus 2)

You think that, but it is in your best interest to know why they did it.

Talk to your adviser and ask why you were kicked out. If it was because of Calc II, then ask if you can get back into the program by retaking and passing the class. If it was some other reason, see if you can be re-admitted by addressing that reason.

How is your GPA? Most schools have minimum GPA requirements. While generally they'll put you on probation for a semester before they kick you out, schools don't have to do this, and they may have kicked you out straight up the moment your GPA slipped too low. That being said, most schools also have a process for re-admittance. Talk to your adviser and find out what this process is. Chances are that if CS is your "dream" major, there's a way to get back into the program-- you just have to figure out what convoluted bureaucratic process you'll need to go through to make it happen.