The eligibility for Merchant Navy is that you must pass your 10+2 with Physics, Chemistry, Mathematics compulsory.

Now as you have PCB and no mathematics then you aren't eligible for the Merchant Navy.

If you want to do Merchant Navy then you can pursue your 10+2 in open schooling with Mathematics at NIOS.

To know more about Merchant Navy visit the link below:

https://www.careers360.com/careers/merchant-navy

To know more about NIOS visit the link below:

https://school.careers360.com/exams/nios-class-12

I hope my answer helps. All the very best for your future endeavors!