You can go with computer science.
Don't think that you are weak you can do anything maths need only practice and patience.
And in further ( BTech studies ). Maths is important in all aspects but it is not that you have to be master in maths . If you know the basics and concepts of mathematics than you can easily cover up .
So don't take this as negatively just choose your branch in which you are interested because there you will learn about core and specific subjects in which basics of mathematics will be needed.
So good luck.

One thing you should keep in mind is that without mathematics engineering cannot be completed therefore if you are weak in mathematics in interested in engineering then you need to make your mathematics very strong also if you failed to do so then you should choose branches which require less mathematical skills such as biological science and bioengineering chemical science technolo but is branches also have some level of mathematics therefore if you can you should improve your mathematics otherwise you also try for some different fields because without mathematics engineering cannot be done.

Practice Mathematics everyday. 

Solve the sums, make notes of formulas and revise the formulas everyday.

There are books which can help you understand mathematics better. 

Some of those books are :- Higher Algebra by Hall and Knight, Problems in Calculus of One Variable by I. A. Maron , R. D Sharma Volume 1 and 2, Co-ordinate geometry by S. L Loney.

Also refer textbooks of Mathematics of your respective 12th standard board. 

If you still have any queries feel free to ask in the comment section down below.