How do i tell my family that i accidentally killed the dog?

my sister just got a puppy for her birthday and i accidentally ran it over with my car the other day. i cant tell my family becaus i just got my license and i dont want them to think im a irresponsble driver. ive been hiding the dog in this old barn on our property for 2 days and evryones wondering where snuggles went. what should i do?