New Job Jitters

So I just started my first real job as an office assistant at this huge corporation. On day one, I thought I had a meeting scheduled with the head of marketing for some critical briefing. Turns out, it was supposed to be a team lunch in the cafeteria! I showed up dressed all professional and ready to take notes, only to find everyone just sitting around chatting over sandwiches. They were all so relaxed and friendly that my nervous energy practically doubled. I spent most of the day overthinking every little interaction and wondering if anyone noticed how out-of-place I felt. Now here’s where it gets even more awkward: when one of my new colleagues asked me about a project we’re supposed to start on Monday, I had no clue what they were talking about. I knew there was something scheduled for that day but completely missed the memo about which part I’m responsible for. How do you tell someone ‘I didn’t read your email and have no idea what we’re doing’ without sounding like an idiot? Do new hires really mess up this much, or am I just overthinking everything? Advice appreciated on how to bounce back from these kinds of missteps.