I have broken my engagement to a sister a few months back. Unfortunately, this was done 2 days after the contract was announced. The actual contract was done 2 months prior. The walima never took place. Many people criticize my action since, she will possibly not marry anymore, as per local culture, and that I have not given her enough time to "adapt". Prior to the separation we had a lengthy discussion on how I need our household to be run. Priority 1 was Islam. After the announcement, she took 2 shots at that concern, things I never mentioned as I assumed they were qualities she had, and I would not have approached her bad what I know now. I paid half the dowry, and we separated. My question: Did I do wrong to the sister? And if so, what can I do to rectify this. Only Allah knows if she will turn better, but I have little hope.

Praise be to Allah, the Lord of the Worlds; and may His blessings and peace be upon our Prophet Muhammad and upon all his Family and Companions.

It is apparent that you took the decision of canceling the marriage contract in hurry.
The period you mentioned was too short to take a proper decision. It was very possible to admonish her and try to change her from bad to good; normally a wife follows her husband. However, what Allah decrees surely it happens. Now, you may correct your mistake by returning to her and being complaisant towards her. Thus, you may take a good step towards a new happy life. We invoke Allah to make her and you steadfast and keep both of you on the right path.
However, if the mistakes you observed in the girl's behaviour were great sins such as mixing with opposite sex or bad character, and you cannot correct them in this case, what you did is correct.
Finally, we would like to inform you that your question is very ambiguous so, we cannot go in more details.
Allah knows best.