Should I get a paternity test?

Ex gf cheated and got pregnant and told me she is keeping it and marrying AP, then said she was unsure of who’s it was and would let me know. After her doctors appointment told me it was AP’s based on the age they gave her.

I haven’t been with her since the middle of October, she said she cheated middle of November. Also told me she had a negative pregnancy test (was in the hospital for a few days after a mental break beginning of November) and a period since we were together.

By her accounts there’s no way (or it’s extremely unlikely) it’s mine. But I have no other proof than her word, which I obviously don’t trust at this point. I asked her about a paternity test and she outright refused and got angry because “there’s no way it could be mine” and she doesn’t want the extra stress.

Should I get a lawyer to try and get a court ordered paternity test after the baby is born? Or should I trust what she is telling me?

EDIT: Thought I should add that the only reason I’m considering is because even on an off chance the child is mine I would want to support it and be a part of its life, despite the mother. Also want to add that we are not and have never been married.