My Little White Lie at Work

So, I recently started this new job as an assistant manager at a local coffee shop. It's my first managerial position and I'm trying to impress everyone with how organized and reliable I am. One day, the store was super busy and we were running low on our most popular espresso drinks. I noticed that one of our baristas, let's call her Sarah, had finished making a drink for herself and there was an extra shot of espresso sitting in the cup next to hers. Now, this isn't allowed because it means that customers aren't getting their full shots, which is a serious thing here. I went over to where she was working and said something like, 'Hey Sarah, I noticed you had some extra shots there earlier.' She looked guilty and replied, 'Oh no, I didn't mean to take that! It's just a tiny bit left over from my own drink. Don't tell anyone, okay?' And then she quickly made another shot for herself. Now, normally I would report this because it's against company policy. But I felt bad because Sarah was already stressed out trying to keep up with the rush. Plus, we're all just tired and overworked, right? So instead of reporting her, I went to my manager and said that there had been a shortage in espresso shots from our supplier for the morning shift. I really hope no one found out about this little white lie because it made me feel guilty afterward. It's not like I didn't know better; I should have reported Sarah immediately. But sometimes you get caught up in the moment and make choices that aren't always ideal.