If you're a non-resident of CA and you never actually (physically) performed any work in CA, then your W-2 income from that work is not subject to CA income tax. If your employer mistakenly withheld CA income tax, then you'll have to submit a non-resident CA tax return on which you report the withholding but allocate zero income to CA, in order to receive a refund of the incorrect withholdings.
Your income is 100% taxable by your resident state of SC, regardless of its source.
**Answers are correct to the best of my ability but do not constitute tax or legal advice.
