If your situation is the same this year, and your employer cannot withhold SC taxes for you, then you should make quarterly estimated tax payments to SC for 2021 so as to avoid another large tax bill next year as well as any possible penalties or interest.
This link contains both the instructions for making those payments online and the necessary forms if you prefer to pay by check:
https://dor.sc.gov/forms-site/Forms/SC1040ES_2021.pdf
It's expected that you'd have a large 2020 tax bill for SC because all your income was taxable by SC and no SC taxes were withheld from your pay. Nor are you eligible for any credit for IN because in effect you paid no taxes to IN (the withheld IN taxes are fully refundable).
**Answers are correct to the best of my ability but do not constitute tax or legal advice.
