I havent touched Optional till now

As Very less time is left for pre(my first attempt ) and I havent touched optional(geology) and modern and ancient history till now.
Should I start doing it parallely now but that would take away precious time from other subjects to revise like polity geography(just did till physical) and economy(just finished vivek singh chapter 4) that i have to revise.. especially polity whjich i read once 6 months back..?? If i dont touch optional then, even if i clear prelims, it will be too less time till mains..
What should I do? What should I study now and what to skip?