I got caught for shoplifting under 5000 in Toronto, Ontario at the age of 20, police were called but no criminal charges were made, I was let go with a warning. I was told to sign a document that explained an act against the retailer. I should not have signed it, but I am aware that I should be getting a civil recovery demand soon. In research it looks like I do not have to pay the fine unless I am sued or receive a "statement of claim". But if I don't pay the civil recovery demand will it affect my credit?

First it is not a "fine" it is a civil penalty, no you do not have to pay it, but they can also still press criminal charges against you. ( and normally will remind you of that)
But yes if you don't pay, they can report it and it will effect your credit.

I got caught for shoplifting under 5000 in Toronto, Ontario at the age of 20, police were called but no criminal charges were made, I was let go with a warning. I was told to sign a document that explained an act against the retailer. I should not have signed it, but I am aware that I should be getting a civil recovery demand soon. In research it looks like I do not have to pay the fine unless I am sued or receive a "statement of claim". But if I don't pay the civil recovery demand will it affect my credit?

This is discussed often - I'd like to see your research because this is not what I've found in the past.

If you don't pay you can and will be arrested and prosecuted. Because you will have backed out on the civil recovery portion, broken your word, you will not be given a second chance.

And, yes, it will go on your credit report as an unpaid debt.