My sister scratched me on my nose 2 days ago. how can i prevent it from leaving a scar?

Scar prevention: It really depends on the depth of the scar--if it is quite superficial it likely won't scar and nasal skin is very thick! your best best is to apply a thin layer of antibiotic ointment twice daily for 5-7 days then stop. Once healed you should avoid sun and use spf 30+ when you are out. A silicone based scar cream with massage will help improve the appearance of scars as well.