i have not secured a good rank in any of the jee exams. should i wait a year to crack any of the jee exams or join another course?

See, you have done poorly in jee exams due to some shortcomings in your 12th subject concepts. I am telling you out of personal experience that its better to go for one more year coaching than to hurry to become an engineer without full interest and confidence.

This is totally personal. If you believe you worked hard and did near your best, then it could be more useful looking at other options. Also, you need to understand what you're good at and choose accordingly. However, if any sickness or other reason hampered your performance you can do well to give

You have some other option also for taking admission in B.Tech. If you are confident enough to crack the JEE than wait for one year otherwise take admission in some good institute.