I Need Advice

I need a little advice...
The mother to my boyfriend’s child is weary about bringing their son around me. I’m all for it. My boyfriend is all for it. We’re planning our future and we want his son to be apart of it. But the mother is already even starting to not let my boyfriend see their kid much either. So besides the fact that he’s going to take her to court at some point, he also wants to get a paternity test. Just to be safe. I just want to know how I can make her feel comfortable with letting me see the little guy. I told him on multiple occasions that I’d bite my tongue around her and be nice even when she’s not when she brings him over for Christmas dinner. And he’s in love with the idea of me being his son’s step mom one day just as I am. But I also want to know if I shouldn’t be too kiss ass with her? Should I tell her how I feel and make her aware that since I’m in my boyfriend’s life, I should be apart of their son’s life too. And make my point clear. Or should I smile and nod, in hopes that she’ll accept me that way too. Either choice, I’m gonna be as nice as expected.
Any advice is greatly appreciated!