If you had received the registration confirmation email in your inbox, then it's very unlikely that the submission confirmation email went to Spam. You probably never got it in the first place. If it was a spam issue, the registration confirmation email would have gone to Spam to begin with. Your best bet is to do as advised already, which is to just put together any other evidence as you seem to have done.
To be safe, you can withdraw your current WP application and apply for the OWP based on the TR-2-PR before your current WP expires on Dec 31. You will still be on implied status, legally, with that OWP application and you can continue on your current job if possible, but you can't switch to another job.
If you keep your current WP application, you can also still apply for the OWP after your current WP is expired on Dec 31, so far your current WP application has not been concluded, and you will still be in legal status but you may or may not be able to continue working.
I think cancelling your current application now and making another OWP application before Dec 31 is the safer option. Also, you can make another application and leave both applications to run concurrently, no harm done.
All these possibilities are listed on this IRCC policy guide that deals with this subject:
https://www.canada.ca/en/immigratio...itors/implied-status-extending-stay.html#sec4