Am I becoming a weak, perfectionist woman?

When I run errands for my mom, I punish myself harshly whenever I: buy the wrong item, couldn't find/get the item she's looking for, or accidentally spend too much of my money (on something for me). Although my mom (when it comes to her items) says it's not big deal, I feel I've made the BIGGEST screw up in history & let everybody down. When I spend too much of my money, I feel like running back to the store & getting a refund on everything just so I can keep that little cash. Help me.....