I'm truly sorry to hear this.... I hope that everything works out well and in your favour
Yes, the Consulate General of Canada office is in Chandigarh.... which is located at SCO# 54-56, Sector 17 A, Chandigarh 160 017.... so you have an interview at this address, right?
When is your interview? Tomorrow? If you still have the time then quickly get the advice of a good immigration lawyer too.... a reliable attorney who deals with Canada immigration/visas..... it would be good if he can help you to quickly draft the letter for the Mauritius entry refusal
I suggest you take the letter drafted by the attorney + a print of the Case Specific Enquiry.... with you to the interview.... and give it to the CIC officials.
If you disclose about the Mauritius entry refusal through the Case Specific Enquiry then you can write something to this effect (a lawyer will draft this in a better way though):
This refers to my online application for Temporary Resident Visa to Canada on date XX, and also to the email request for submitting my passport. I had submitted my passport on date XX as requested by CIC.
I understand that the final decision has not been taken on my visa application, and furthermore, I have not been granted a TRV as yet.
Before a decision is made on my visa application, I wish to disclose the refusal of entry to Mauritius on date XX. The complete truth and facts of this matter are as follows:
Give all details details details/reasons
I had inadvertently erred in providing this additional information about the Mauritius entry refusal earlier, and this mistake on my part was purely due to oversight. It was completely unintentional.
All other information and details in my TRV application are true, complete and honest. I had prepared the visa application to the best of my abilities.
I wish to state that I have disclosed the information of the Mauritius entry refusal to CIC of my own accord and my free will. Further, as a law abiding citizen, I realized this was a genuine mistake on my part only yesterday. Hence, I wish to provide this additional information before a decision is made on my visa application. At no point in time, did CIC ask me to provide any information about the Mauritius entry refusal....." etc etc
As for the Case Specific Enquiry form, the link for New Delhi is: https://secure.cic.gc.ca/enquiries-renseignements/case-cas-eng.aspx?mission=new%20delhi