After sex throw condom in toilet gf picked it up inserted it inverted with semen into vagina, possible chances of preagnancy?

Discarded condom. She stands a good chance of becoming pregnant.
Legally the Father. It would be odd for this to turn into a pregnancy, but not impossible. She is putting you at extreme risk financially if she get's pregnant. You would be considered the father and be liable in the eyes of the law for this child should she get pregnant.