I think you will need to give more details. Did you make a note of the PNR when it came up on screen? If so then this should work:
ba.com/receipt
alternatively RAM/ Finnair (particularly their email link), Qantas etc will give you the information.

If you did not take down the PNR then you will need to call to get that PNR, and then use the tools above. It's not unusual, if booked on a Sunday night, for emails to arrive a bit late. If this a booking outside of self-serve then it can take a number of days since it willl need manual ticketing. If you are on the BA app / included your BAEC number then it may show up there.