You might as well end it all now. Ife is over man. Fuck it all. :D
Nah, I'm kidding. Every teenager goes through this when they fear of being caught. It's not the end for you. It's the end of an era where hiding your smoking will be done, but the end? No way.
I'd just tell them. My parents told me they got more mad when they found out about something, but I continued hiding it from them, even though they knew. Parents hate that and that's why they get mad. If I were a parent, my kid could smoke pot if they wanted to. As long as they went to school everyday and kept their grades up.
So I'd just get it over with and tell them.