Hello,
I am not an expert but I just want to say that I don't have access to your specific application or documents, but I can provide some general guidance.
It is important to carefully read and follow the instructions provided by the Canadian immigration authorities when submitting your application. If you have missed a required document or made an error in your application, you may be able to correct it by submitting a letter of explanation or by contacting Immigration, Refugees and Citizenship Canada (IRCC) directly to request guidance on how to proceed.
In regards to your situation, it is possible that you can still provide the letter stating that you are a CEC invitee to IRCC. You should submit the letter as soon as possible to avoid any potential delays or complications in the processing of your application. You may also consider submitting an explanation letter detailing the mistake and any steps you have taken to correct it.
Overall, it's always best to be thorough and double-check your application before submitting it to IRCC. If you have any further concerns or questions, you may want to seek the advice of an immigration lawyer or consultant.