My bf finished near my breast and few mins after i went to shower. can they drip down and go inside my vagina? i'm stressed that i might be pregnant

No worries: Salmon swim upstream to the same area where they hatched. Sperm are so small that you can't even see one with a magnifying glass. Being in the shower means the water is coming down from above, at 2 gallons per minute, unless it's one of those fancy Jacuzzi showers with water going sideways. Anyway, sperm are not salmon and cannot swim upriver to migrate into a vagina for spawning. No worries.