This is all Pia's plan. She drugged Jai.. and then she took him to the room hugged him and kissed him... and the next thing we knw is that Jai waking up in Pia's bed... and then Jai doesnt even remember what exactly happened that night... Coz nothing did!!! Nothing happened that night... Pia has framed Jai and has made up the whole scenario seem as if something happened that night...
And about the baby... there can be 2 possibilities... either she isnt pregnant atall or else its Pushkar's baby... she is just using the baby as a weapon against Jai...