If you wash your hands with antibacterial soap after cleaning sperm and then finger your girlfriend can she still get pregnant?
Semen that contains sperm dries very quickly on the skin. Sperm prefer fluid at a certain pH and temperature. Washing your hands thoroughly removes semen (and sperm) so it is not on your fingers. Remember to use a condom, though, if you have sex.
No, once sperm has touched the outside air for one reason or another, it generally dies. There is little chance of getting pregnant.
You probably don't even need the antibacterical soap, just regular soap will do fine.