The chances are
very slim, I wouldn't worry too much. If you ejaculated onto your breifs, the semen would die soon afer being exposed, and generally sperm needs to be projected into the vaginal canal for it to have a chance at fertilising the egg.
There
is a chance, but extremely unlikely. If her period is late, get her to do a home pregnancy test for peace of mind. I assure you, don't stress!
Take care
Tyger.