Hello!Subham 

Your Percentile is too low.Cuttoff percentile are going to expect around 85 under general quota.40 percentile is too low even with this score you won't get qualify for advance 2019.You still have one attempt for jee mains 2019.You have lot of time in it.Practice as much possible.Solve previous year paper.And go through every formula.Secure a seat in NITs this time.

You can ask if you have any other queries.

GOOD LUCK!

The approximate rank for percentile 40 will be around 525000(+-). Note that this is just an estimation and it can change after JEE Mains is again conducted in April depending upon number of students appearing for it. 

Now, I'm sorry to inform you but in this percentile it is near to not possible to get admission in engineering through general category.

JEE Mains is again going to be conducted in April. You have an opportunity to give JEE Mains again in April and improve your score.

If you still have any queries feel free to ask in the comment section down below.