Can someone go to the bank?

I'm an assistant manager in an extremely understaffed store. I only had one driver until 5pm. My opening driver comes in an hour before the store opens to prep sauces, sandwich bread and desserts. I realized the till was short on cash shortly before it was time to open, no five or ten dollar bills whatsoever. Our bank is about twenty minutes away, outside of our delivery area. My only driver steadily stayed on the road taking runs all day. I had nobody else to send to the bank. The newly appointed general manager came in around 4pm, gets pissed about the till, and asked "What's more important? Prep work or cash?" I said that I figured they were equally important. He threatened to take me off the schedule because of it. I apologized and said that it wouldn't happen again... Seems a bit harsh considering we've never had a conversation about this before. I have been with the company on and off over two decades. I rarely call in, show up on time, do more than my fair share of work, and stay late nearly every shift. Plus, I've never been written up. I'm honestly just shocked... I was off work yesterday. Normally, when I check out drivers, I ask for their small bills. I wonder why yesterday's management didn't bother doing the same to prevent this... Is my GM overreacting or am I completely at fault?