This could be a comment but. . .
In all seriousness, probably the best help anyone can give you is "read the manual." Since we don't have access to your data, I am guessing that pages 39- 40 of the manual will help you.
Also I could point you to the rattle package: this is a pretty simple point and click interface to the rpart package, along with several other modeling tools.
By the way: as noted on the 2nd page of the manual, CART is a trademarked name. "Recursive Partitioning" is a generic name, so you should probably describe your model accordingly.
I hope this helps.