Crossing the border

My boyfriend and his family (I am a US Citizen and they all are Canadian) want to cross the Canadian border soon. I am staying with his family on a visitors visa currently. However..here's the worry that I was thinking of: I have applied for a visitors exension and was refused. I've heard that the immigration officers put a red flag on those who have been refused entry to Canada. Would a visa refusal be a red flag and prevent me from coming back into Canada? They all want to go shopping and I want to come with them.

I live in London with my mother(Dual citizen), would it also help if she hand wrote a letter out saying that I live and work with her, because I do. I have full intentions of returning home. It's just the visa extension refusals that I'm scared might raise a red flag.