New staff pharmacist struggling with expectations

I am a relatively new staff pharmacist at a low-volume Walmart pharmacy. On weekdays, we typically fill about 210-250 scripts per day, and on weekends, it's around 125 scripts on Saturday and Sunday.

At my store, there's usually just one pharmacist working each day, except for Mondays when we have six hours of overlap. I've been working for eight consecutive days now.

Last Friday (Day 5 of this stretch), I gave seven vaccines, three of which were for new patients to Walmart. However, over the weekend, we were overwhelmed with pickups. Our total end-of-day sales hit almost 320 for both Saturday and Sunday. It was so busy that I barely had time to think about giving vaccines. On weekends, it's just me as the pharmacist and one technician, who isn’t certified to administer vaccines (not her fault).

My manager emailed me, questioning why I didn’t give any vaccines this past weekend. Honestly, I’m a bit frustrated. As a new pharmacist, I’m doing my best to manage everything, avoid mistakes, and keep my license safe. For context, I’ve already caught three errors made by other pharmacists in my first month here.

Any advice on how to handle this situation?