GATE

It is a very good option and the most easiest way to get selected in PSUs. You just have to give a year with full dedication. The next year, you will see yourself in top firms.
Apart from this, you can even go for higher studies like M.Tech as it helps to open lots of career opportunities.

Give mock tests as much as you can and find the topics of strong and weak zone, and then take assistance from your teachers, seniors, juniors, etc. to cover your weak zone. Slowly but gradually increase your effective study hours. Last but not the least, don't let your preparation down.

Hello Varsha,
I think you should start preparing for GATE exam in 5th semester then you can easily qualify for top colleges.
All the best.

There is a lot of difference between JEE and GATE. JEE is an exam conducted to get entrance to any engineering college whereas GATE is an exam conducted for entrance in PSU, or for M.Tech.

Yes, you can as if you are an electrical or mechanical engineer then you get a chance to get job in the Indian railways, but you have to score good marks in the GATE exam.

Hello Karan,
Yes, droppers are also eligible for GATE exam as this exam is both for job and for higher studies, so you have to score good to get selected.
All the best.

No, you are not eligible for GATE with B.Sc in electronics (3 years). If your B.Sc is of 4 year duration then you are eligible otherwise after M.Sc you are eligible. Visit the link: http://www.gate.iitr.ernet.in/?page_id=266

JEE Mains is just a beginning. GATE is the advanced version of JEE Mains but it is a bit easier than JEE Mains.