As someone who lived in a web of lies built upon lies built upon lies and more and more lies for many years, I very much encourage you to come clean with them right now. The lying will only get worse and never knowing when that other shoe is going to drop is a HORRIBLE way to live life.
And I hope you take this as a wake up call to stop the pot smoking too. Just like the lies, the trouble your smoking can cause will only get worse. You got out of the legal jam this time but probably won't be so lucky next time.
My drug of choice was alcohol. I was coming home from a bar in September 2004 absolutely hammered out of my mind, having absolutely no business driving. A cop stopped me. Instead of arresting me, he gave me the option of leaving my car parked right where it was and calling someone for a ride home. I called a cab. That should have been a wake up call. Instead, three weeks later I was coming home from the same bar and crashed my car into the side of a house a few blocks from my own house. The arresting officer was the same one who'd let me off the hook three weeks earlier.