Can I deposit unutilized amount in CGAS to claim exemption u/s 54EC?

No. If you want to claim exemption under section 54EC, either you have to buy Bonds in the same year within 6 months from the date of transfer of the asset or you have to claim exemption under any other section by making some other form of investment. For the purpose of claiming exemption under section 54EC by purchasing bonds of REC or NHAI, unutilized amount of capital gains can not be deposited in Capital Gain deposit Account Scheme of a bank.