I'm going to tell my father that his step-daughter snuck marijuana into his house without him knowing.
Do you know how she managed to bring dope into the house?
I bought groceries and my step-sister hid the weed among the groceries to get them in the house.
I understand that you are upset with your step-sister for tricking you into bringing dope in the house, but telling on her to your dad makes you look weak. Confront your step-sister about it directly and handle the issue yourself.
I feel like this makes me look bad to my father so I want to show her how I can make her look bad.
You have every right to feel upset at your step-sister, but you don't look bad to your father as he isn't aware of the issues. Telling on her runs a great risk of causing major issues within your family. Have you considered all outcomes, as some might be negative for you.