Lol take a deep breath. You're fine. It's not like a huge mistake on your application, it sounds like you just left something out. One EC isn't going to make or break you. If you're worried about emailing them and seeming like you didn't follow directions, don't worry about that either. They won't deny you interviews or an acceptance because of this at all, which is all that matters. Don't get lost in the small things that won't matter too much either way. 🙂 You're fine!