Excuse my question but, how likely am i to become pregnant if he came on the entrance of my vagina but not inside? can the sperm get inside by itself?

Very unlikely: Anything's possible, but that would be a long way to swim for the little guys. Also, one would need a lot of vaginal moisture all the way to the outside so that the sperm wouldn't have to attempt swimming across any dry spots. This is assuming that the penis never made it into the woman's body (and isn't an episode of the "pull-out" method).