Your performance in 12th standard maths won't directly affect your placements after B.Tech (CSE) as long as you meet the eligibility criteria for the B.Tech program itself (which typically doesn't consider 12th maths). Companies focus on your B.Tech academic performance, projects, internships and relevant skills during placements.

Pursuing a CSE diploma is a great option to gain technical knowledge and industry exposure before a B.Tech. This can be especially helpful if you want to strengthen your fundamentals before entering the B.Tech program.

Strive to excel in your B.Tech (CSE) program. Pay close attention to core subjects, participate in projects, and consider internships to gain practical experience. This will make your profile stand out to potential employers.

Enhance your programming skills, problem-solving abilities, and stay updated with the latest technologies in demand for CSE graduates. Building a strong portfolio showcasing your projects can be a major plus.

I hope it helps!