Condom slipped half off leaving cum on penis. Could it have came off inside her? And after pulling out rubbed on her with cum on it pregnancy chance?

A small chance. There's a small chance of pregnancy. A urine pregnancy test, done correctly, gives a reliable result 3 weeks after sex (3 weeks after when conception might have occurred), or 1 week after missing a period. If done sooner, a positive result is likely real, but a negative result may be due to testing too soon. If a woman gets her normal regular period, then she is not pregnant.