you can apply it next time as registrations for gate exam has been closed. But make sure your backlogs should be clear. Remember one thing GATE isn't easy so think wisely about your choices. 

 for further details check this link given below:

https://engineering.careers360.com/exams/gate

thankyou.

Registration for GATE 2019 is closed. If you have a backlog then also you can apply for GATE, But you should keep in mind that while taking admission into M, Tech Programmes all your Backlogs must be cleared. But this time you failed to register for GATE, try next year.