Since you applied through BC-E category, you will get a lot more advantages than other candidates. Considering past year records, you will be able to get Computer Science in JNTUK with your rank. As mechanical branch of JNTUK is considered better than other branches, it will be difficult for you to get in mechanical branch with this rank.

One more thing I want to suggest, take admission in a branch which suits your interest, not in a branch which promises huge pay packages and high placement. If you choose according to your interest and do hard work, then you will be successful no matter what your stream or college is.