GST refund of FY 2017-18

Can an assessee can claim GST refund of FY 2017-18 for the wrong RCM tax paid in CGST and SGST instead of paying it as IGST and such IGST has been paid at time of filing of Annual Return via DRC -03.
Time limit for claiming of all refund is 2 years from relevant date but is there any extention of due date for filing the application of refund in case GST paid in wrong head.