should I tell the truth?

Long story short I took money from my moms hidden money to buy myself plan b. My parents don't know I'm sexually active.. I had to act fast to get the plan b. I'm afraid my mom will notice money is missing. If she finds out do I tell her the truth of how I'm sexually active and had an accident that could have gotten me pregnant or should I pretend I don't know the money was even there and tell her she miss counted? What would u guys do in this situation