As you want to get the details that will you be able to give the exam of GATE if you complete your degree in 5 years so here is the information of the same for you:

You are eligible for the gate exam ,there is no such rule which tells that the students should complete the degree in four years inly to be eligible for the GATE exam

There is no limit for the number of attempts so do not worry and attempt the gate exam,

If you get an good rank you will have chance to improve the value of your education by studying in the IITS and nullifying the effect of back logs in engineering