If you wrote this far, you definitely have some good ideas. A potential conflict is an underestimation of how many people will show up tomorrow. Example: As Watson traveled back to Sherlock's berry store, he received a call. "Sorry to interrupt, but some more costumers called in recently. I forgot to tell you, as I've been busy planning for tomorrow. Is there any chance you could pick up more berries?"
This would create a conflict in which Watson would have to hurriedly search other stores in need of plump, delicious blueberries, or collect the ones from the pine, which Sherlock specifically advised against. Thus, later in the story, creating a conflict (scene) between Watson and Sherlock, or the store and the costumers.
