Calling off engagement

I had to engaged with a girl which I did not like due to family reason. Earlier I thought I would adjust with her, but after a long period of 10 month, she did not turned up as the girl I wanted in my life. She always think about her not me. She has a nature off showing off, but I wanted a simple girl which will be with me in every up and down of my life.I told my family several times that I would not be happy with her in future, but they are saying now nothing will happen as I am already engaged with her and her family can do a legal obligation. For information, only ring has been exchanged and we never met alone in this period. The marriage has been scheduled in the month of April 2012. I am very firmed about not to marry her.
Please let me know if they can sue me or my family in court or, make a police complaint if I refuse to marry. Kindly help.