I'm good in Chem & maths but not in Phy & since I want a govt job , I'm going for civil engineering ... Will it b OK ??

In college I had multiple classes I did not see where I would ever use them in my career.  When I asked the professor why we had to take them he said "You take those classes to teach you how to think."  Even in a government job you will be required to do the job efficiently and correctly.  Civil engineering is a board discipline and covers many aspects such as environmental, geotechnical, and structural.  Physic and Science as well as biology all play a role in those disciplines.  You may go into a an aspect of civil engineering where they are not a major factor but they are still there.  Being "good" at something is relative.  And as you continue to study you may find portions of the different science classes your are "very good" in and other not so much.  Just work hard and ask the teacher and other students for help when needed.  If you put your mind to achieving a goal you can do it.