You career options after 12th depend upon whether you've taken PCM or PCB. In case of PCM, you can go for an MBA, BCA and then an MCA, you can also go for law,designing,journalism even though you've chosen science as a stream. Also, you can go for architecture.Pharmacy is also a good option in case of PCM or PCB.In case of PCB, you can go for research work, biochemistry, biotechnology etc. Also, you can do your B.Sc. Followed by M.Sc. With your favourite subject.You can also go for HR or counselling.Thus, with the science stream you can take up career options of the other streams as well.
If you r not getting admission in engineering colleges then go for any other field. Which you like d most like MBA & don"t take any tension be free. You vil definetly get it somewhere