Hi Moon 

Yes you are eligible to appear for NEET 2018.

As per CBSE NEET eligibility criteria, it is necessary to have Mathematics as a subject in Class 11th and 12th, along with PCB and English, but CBSE doesn't necessitate passing in Mathematics.

As per the marks requirements of CBSE NEET, candidates appearing in NEET UG are required to pass in PCB and English subjects individually, and,

Should acquire at least 50% marks (40% in case of SC/ST/OBC) in aggregate in PCB.

As for grace marks, it won’t make a difference. The bottom line is, you should have got at least 50% in PCB together.

I hope it clears the picture for you.

All the best!