Engineering

You have not written about the state where you wish to pursue B.Tech course. However, on the basis of your 12th marks you can get admission in B.Tech courses in the following universities.
1. LPU Phagwara
2. SRM University
3. Chandigarh University

You have to apply through both of the admission streams as described below in SASTRA.
Stream-1 (JEE Main+!2th Marks) : 70% of seats will be filled through this stream. 25% and 75% of weightage are given to JEE Main and 12th marks respectively.
Stream-2 (12th marks based) : 30% of seats will be filled through this stream and 100% of weightage is given to 12th marks. So you have good chances of admission through stream-2.

Yes, you can get Nirma University through GUJCET. The fifty percent seats of the total sanctioned seats shall be filled as Government seats from the candidates who have passed the Qualifying Examination from the schools located in the State of Gujarat and have appeared in GUJCET Examination for the corresponding academic year, by the Admission Committee on the basis of the merit list prepared by the Admission Committee.
The rank below the 500 in GUJCET can be good enough for admission here in the desired course.

The last date for submission of online applications for Andhra Pradesh EAMCET has been extended up to 17.04.2020. While the EAMCET exam dates 20.04.2020 & 21.04.2020, 22.04.2020 & 23.04.2020 has been cancelled. The new exam dates has not been declared so far. Hence, wait for some time and keep in contact with EAMCET website:
https://sche.ap.gov.in/EAMCET/EamcetHomePages/Home.aspx.

You have not write about the College, where you wish to pursue the B.Tech CSE course. However, in most of the Colleges the eligibility criteria is 12th with PCM with at least 50-60% of aggregate marks+Entrance exam. While the eligibility criteria for top leading government. Institutes like IITs, NITs and CFTIs is 75% marks in 12th+ JEE Main or JEE Advance exams. Private institutes like VIT, SRM, LPU, AMITY, Chandigarh University, etc. conduct their own entrance exam for B.Tech admissions. So tell me about the college name for further details.