Hi

You don't need to worry dear both your certificates are valid.

Just because now you are going to appear again for board examination with mathematics as a private candidate doesn't mean that the previous class 12th passing certificate  becomes invalid , so both certificate i.e with maths and Biology are valid.

So you are definitely eligible for Neet examination provided

you mu st have passed in English and in both the theory and practical  of PCB i.e Physics, Chemistry and Biology with at least  50  % in aggregate of PCB ( in theory +practical) in 12th examination  if you belong to general category , or   at least  40%  in aggregate of PCB if belongs to  Obc/ Sc /st

For detailed information about neet examination go through our page for which link is provided below; -

https://medicine.careers360.com/articles/neet/amp

Thank you