Hello. I have had a city for a long time. It is one of the most stable cars assembled in pakistan. (Before anyone gets offended, i said "one of the most"). You should get your car checked. There seems to be a problem with either the suspension or the tyre speed rating. My car reaches 180 kmph without even the slightest feeling of unstability.
And to the people who will criticize my comment, i have owned several cars and city is VERY stable (after civic ofcourse).