I’m in deep sh**

So my sister told me my parents had found my contraband such as my vape and alcohol and then sure enough my dad said we needed to talk tomorrow. He and my mom don’t know that I know. I’m 17 and knew that my bad decisions would catch up with me at some point but now that they know I really just need to prepare myself. I don’t do it a lot, maybe once a month maybe. Any suggestions on how to soften the blow??