Hey,

Hope you are doing well.

Well for opting btech fir a career option  you must have qualified your 12th in pcm with more than 50%. But as your jee main rank is 8 lakh around because of which it is  quite not possible for you  to get admission in cse branch  of any reputated college . But dint loose your hope still there are many colleges and universities who actually fullfil this dream of many students . You can easily apply to those private universities and college with cse branch. Colleges in mumbai where tou can take admission :

1. MPSTME MUMBAI

2.VESIT college of engineering.

3. SPIT college of engineering etc.

Hope this will help you