Ask what happened. You are at an informational disadvantage and, if you aren't lying or leaving anything out, you didn't do anything wrong. Just explain "hey I was stoned and have no clue what you were saying" to the dealer and the cousin, see what both say, and fix whatever problem there might be. They'll understand you were stoned, on account of they sold you weed. Contact both and if the stories don't match up be suspicious. Otherwise, it's business as usual.