My Big Mistake at Work

So today was my first day on the job, and I thought everything was going well. Then, in a moment of panic when my boss asked me to do something really simple, like, tell him what tasks were due this week?, I froze up. Instead of just saying I wasn't sure and asking for help, I said yes, I knew exactly what to do. Big mistake. Now I have to pretend like I know everything while secretly scrambling behind the scenes to figure out where all these assignments are and how to catch up on them. Why did I think lying was a good idea? I should’ve just been honest from the start.