Having PCM and Economics as my subjects, is it gonna be difficult for me to pursue management and aim for IIM?

Keya, Not at all, infact the combination of PCM or simply speaking "the science stream"students have been quite successful in cracking the CAT exam and even topping it in past few years and presently too, there are many science stream students pursuing their bachelor's degrees in pure science and aiming for the IIMs and preparing themselves for management courses, so there is nothing different or difficult for a PCM student to pursue management. Infact, you having Economics as an additional subject would make it even feasible for you to opt for management as then you would have some elemental knowledge of economics but I have seen many students who hadn't even read economics till after their graduations and had pursued management as their career. So, it all boils down to what you feel would be accurate for you taking into consideration your interest and passion.

Additionally, the MBA or the PGDM courses don't require any bachelor's degree in management in order to be eligible for applying for MBA, rather it requires a candidate to be graduate in any discipline along with a set percentage in graduation in order to be eligible for applying to the Master's courses in management and therefore, any person from any discipline or any stream can apply for the same and has equal chance of clearing the entrance exam to pursue management than another person who has a management background.

Therefore, you should not worry about the chances of facing difficulties rather focus on enriching your knowledge and analysing what your interests are.