How likely is it for me to get pregnant on the day my period ended and i took a plan after pill 4 hours after having sex?

Unlikely: Sperm can live for 48-72 hours in the female genital tract and can fertilize an egg if ovulation happens. If intercourse happened close to ovulation, than yes, there is a chance. Since intercourse took place many days before your expected ovulation and since you took plan b, pregnancy is unlikely.

Unlikely: You should be safe, but consider using birth control.