Go through the below-provided link to check the answer key of JEE Main 2018:-

Link for all sets question paper and answer key:- https://engineering.careers360.com/articles/jee-main-answer-key

The correct responses in the answer key have to be compared to the response sheet of yours.

You must follow the official marking scheme to calculate your probable scores of JEE Main 2018.

Correct answer:- +4 marks

Wrong answer:- -1 mark

If you have calculated your JEE Main scores, go through the Carers360 rank predict to predict your ranks.

Link to the page:- https://engineering.careers360.com/-articles/jee-main-rank-predictor

( However, You have to remember that the data may not be completely correct in nature. )

All the very best and good luck.

Rahul according to last year cut-off which was 49 marks for OBC category you can definitely get a chance to appear in JEE advanced examination but we can't be sure about until JEE Mains 2018 official cut-off is announced which will be most probably will be done in 24th April. But I will recommend instead of waiting for the cut-off announcement you should be optimistic and keep on going with your JEE Advance exam preparations because with your 66 marks you will be getting AIR around 250000 which will make it very difficult for you to get a good engineering college even within OBC category.

Feel free to ask if you have any more queries. All the best!!