See step one and don’t freak out! Everyone makes mistakes, but maybe this one was a bit bigger. Make it clear that you care that you fudged something. Don’t make excuses, be accountable for what you’re responsible for and then go home and eat an entire container of Ben & Jerry’s Ice Cream. Then really think about why you made that mistake? Has it been a persistent problem?
Try to figure out why you dropped the ball. Time management? Lack of clarity? A miscommunication? Once you know what it is try to make a plan that can address your weaknesses.
Whether it’s getting a daily planner or taking better notes, you’ll want to know what makes your brain fart now before you get a real job.