How can I be a better stocker at my job? [I Hate That Feeling Of Not Being Good Enough]

It sucks when you start a new job and think it’s going fine until the store makes changes and you work from during the day shift to working the overnight shift. There are no longer day stockers so overnight is in charge of all stocking now and they get a raise so of course I took it but now my manager says I need to get better in order to keep working overnight. I felt like I was doing good enough I hate feeling like this..