Can i Cancel Enagagement?

I had engaged with my girlfriend having relationship with her since 1 year before and then we engaged and we told we will marry after one year and now its about 10 months since our engagement .We have all decided the dates which is after 4 months for marriage. But before 3 months from now she had undergone an operation of syst and there are pregnancy complications in that operation which was hidden by their family from my parents ,only i knew about that problem. Then everyday she was demanding things from me and i got angry and thought i am cheating my parents by not telling her that she has an operation of SYST. And important fact to note that when i went to hospital at the time of hospital her mother told me not to tell to my mom.Now i told it realising that it was wrong so my mom called her mom and told that u lied to us,etc.She said sorry & all and we have asked for medical reports now.Further she is also having potential problem of white skin patches that her grandfather and buha has,meaning thereby that she may get it because some very light patches can be seen on her hand and back. I dont want to marry such a girl mainly because of her nature and her thirst for things that her family cannot afford.And please note we had intercourse between this period and she had a boyfriend too earlier than me with whom she had done many times. I dont like her please suggest. And i have saved a whats app chat in which she only said that we will have sex. Many times she took leave from office and we went to hotel also. Advice me how to approach for cancellation.We have not taken any money from her except cover that their family gives on roka ceremony and we have not demanded dowry and all anytime and we have also given gifts to her. Please advice properly because i am worried about whether they will go legal. I dont want to suffer all that stuff of legal.But to be frank i am not interested in marriage at all now.Please help very properly