hi,

see admission to IIM  would be solely based on cat score, candidates academic record, year of working experience and so on. however there is no particular provision like mathematics marks would be scrutinize. if you have declared pass certificates from your institute and has accepted the certificate in university education like bachelors degree, then there is no use again to apply for 12th course. however if you have time permits and can appear for only maths paper then you may go for it. however to admission in iims cutoff score varies and depends on candidates category. your academic profile is not very strong , you need to score very high in CAT exam.

at the end I would say never loose hope, there is many other institute which offer mba other than iim , has excellent placement also.some of the institute are as follows:

xaviours  institute of management , jamshedpur,

fms delhi,

Indian institute of foreign trade ,

IMT ghaziabad,

MDI gurgaon.