Section 54(3) deals with refund of balance lying in ECL (Electronic Credit Ledger). Refund of unutilized ITC credit will be allowed under following cases only:
Zero rated supplies:
Export of goods and services under bond or Letter of undertaking (LUT), without payment of IGST
Supply of goods or services or both to SEZ developer or a SEZ unit.
Inverted duty structure (i.e rate of GST on Inputs are higher than that on output) (other than nil rated or fully exempt supplies), (excluding notified supplies for which unutilized ITC is not allowed)
Therefore, you can claim refund of SGST only if you fulfill the above-mentioned conditions.