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Your partner is sponsoring you . You don't have to worry till you are given notice of anything. It was an honest mistake and you didn't misinterpret just to get to Canada, you are even a US citizen. so don't worry too much and try not to be affected by negativity.
 
:-[

I HAVE to mail this application by Wednesday, my police certificate is about to expire. I think the only think I can do is wait and see what happens and seriously hope for the best.

I felt so good about my application until I realized all this.

Hopefully, because I have everything else in order, so much proof of our relationship since 2008, my medical done, my fees paid, my police check included, everything else perfect, they'll see that I made a mistake.

It's a lot to hope for but what's done is done.
 
I suggest attaching a letter explaining the situation. I had something similar (sorry I can't remember the exact details) but I had checked single status on something and later changed it to common law. .

They are humans, not robots - at least I hope not :o) - and realise people make mistakes. I wouldn't worry. Seriously.

Write the letter - typed - and address it to whomever, and attach it to your form. You'd be surprised how simple it is.

Secondly, you can do what I did and call the call centre as you are in land (who was the one that informed me to write the letter and attach it to my application) and explain what happened and take their advice. To be honest, the know better than any of us on this forum.

...so, breathe! and call the Call centre...

:o)