I slept with a girl who a month later told me she was having a baby and it was mine, what do i do?

Ok this is it, back in august last year around the end I met a girl on a night out, exchanged numbers etc. We met up the week after and the week after that, slept together, she told me she was on the pill the second time in the morning she said she wasnt on the pill so itold her to get a morning after pill.A month later she txts me sayin is having a baby and its mine. At the timeI had met someone else who I had started a relationship with. I knew the best thing was to be there for the baby. I stayed with my current girlfriend though. I wasnt allowed to any of the scans, hospital appointments, and after xmas mid january i recieved an email stating the baby wasnt mine it was someone she slept with about 2 weeks b4 me on holiday, and she wanted me to be a father to it, as she liked me. I rang up her father who told me he was ashamed, they told me to move on. she is apparently due on the 15 may, cud be earlier? and she was on hol to the 7th aug, wen did she concieve? what shall i do?