Only final year and pass out students are eligible for Gate. As you are in 3 year, you cannot write Gate exam. So as of now it is advisable to make your basic concepts clear because this will be helpful for your Gate preparation as well.

To know the Gate eligibility criteria in detail, you can go through below link -

http://www.engineering.careers360.com/articles/gate-2017-eligibility-criteria

Good Luck!!!