Is it fair to expect one person to run drive through and lobby alone efficiently?

I've been working at mcdonalds for 3 months but put in my two weeks a week ago. Some might say I shouldn't care since I'm leaving soon, but I want to leave on good terms and get a good reference. I close with the gm most nights. We get along real well, but sometimes ge gets visibly frustrated with me. Like, last night he was on line cooking the orders. Someone was at first window cashing people out. The drive through line was very long and a lot of people just showed up in the lobby. I had to give out orders in at the second window, and the lobby. Most of the time people just order at the kiosk so I dont have to take their order myself, but sometimes people have a huge order they insist on placing at the counter. I was trying my best to make lobby and drive through happy, but there were people bitching on both sides. I admit. I was taking a long time to get their orders out, but like I said I was trying my best. So I was taking a big ass order at the counter "which I'm not very good at" and I heard my gm tell my co worker cashing out at first window to go help Joe because the drive through isn't moving, and the orders on the screen were starting to disappear because they were in line for so long. After I was done taking the dude order, I walk by my gm, and say that im sorry but I was taking orders at the front counter. He just stayed silent with a scowl on his face. He's usually like "no worries buddy". Thats how I knew he was pissed. We made it through though, and he was back to his normal self. I just wanna know if it should be expected for me to run the whole front end effectively all by myself?

Is it fair to expect one person to run drive through and lobby alone efficiently?
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