What most likely happened is your girlfriend stopped taking BC behind your back knowing you didn't want kids, but hoping once it became real that you were pregnant you would step up like the guys in the TV shows she watches.

If you were using condoms and she was really using BC, there's a less than 1/100 chance the conception happened accidentally.

It turns out her little bet backfired on you, and now she's calling in her family for her. All they know is what she's told them and if their reaction is to be extremely angry and harass you, that should give you an idea what version of the story she told them.

You need to get restraining orders against the family and let your GF know you won't be signing the birth certificate without a paternity test. If the child is yours, sorry, you're on the hook for child support. It's not fair, but it's true. Despite everything she did it's still not OK to pressure her to have an abortion or an adoption. You just need to make it clear you are not going to be in the picture. In her mind, you were going to come around eventually, when she sees you will not that could potentially change her calculus.

Around the late 20s some women start to have very strong anxiety over whether they will ever have children. It's sadly super common for women to do what your girlfriend has done. Good luck to you, bud.