Haven't read whole thread, but it it's not too late, I'd take a screen shot of the shopping list on amazon, or try and get a copy of the order/invoice whatever.
I think it would be hugely unjust for you to end up a father, if you have been tricked into it, when your girlfriend is completely aware of your feelings on the matter.
If I had knowingly tricked a partner into having a baby against his expressed wishes (which only a selfish nutcase would do,) I certainly would not be pursuing him for maintenance payments. If she's that much of a headcase, she might just do that, if you are unfortunate enough to have already unwittingly helped to get pregnant.
I'd deliberately bring up the conversation, tell her again how you feel, and then later send her a follow up text too, saying something like, "You do understand how I feel about not wanting a child, don't you?" which might result in her sending a text back acknowledging your feelings on the matter.
After all of that, I'd confront her. Have the conversation and text asap, before she drops the bombshell that she doesn't know how, but she's pregnant. I bet she'll say she was on antibiotics, and didn't know she needed to use extra protection, or something like that.
FFS, this is a very long winded way of saying, she's possibly already pregnant...she's weird...if she's pregnant you're going to get stung for maintenance for the next 18 years (presuming after a stunt like this you won't want her to be your life partner,) if I were you, I'd want to be able to prove in a court (if it comes to that,) that you were tricked into this...there! (I'll get flamed for this, I bet!)