CAT

Tick over the 'yes' option.
Make sure to clear that backlog in your final year.

If one starts preparing for CAT during the final year of graduation, he/she will have enough time to prepare.

Before submitting the paper, you get the chance of changing your answer at any point of time.

That cannot be predicted.
It totally depends upon your understanding of the subject.

Though you will manage to get a decent college with such percentile. But, if you believe you can score better, then undoubtedly aim again.

Hello Aakash,
These days, most of the colleges offer guarantee of 100% placement, but what matters is the quality of job.
Either you get a package of INR 2 lakhs or INR 20 lakhs, in both the cases you will be called as placed. But, what matters is will it be worth.
So, don't go for such 'guaranteed placement trap'.
Also, with 85% marks, you will be able to crack decent colleges.
And, the job you will get from there will totally depend upon your intelligence, understanding of the subject, etc.

The time span doesn't really matter, but the dedication matters.
CAT is not an easy nut to crack.
You will have to give your best to pass through it with flying colors.
MAT is an easy option as its difficulty level is below CAT.