Confusion about understanding reduced price stickers

I was working as a cashier at a retail store. I was scanning a reduced cake from the bakery department. I was confused about the price stickers on the packaging because I thought it was ringing up the incorrectly. I think that the reduced sticker said $8.99 OFF and I thought that was the price of the cake. I had a customer service manager (CSM) come to my register to help me with this transaction. I started explaining the problem to the CSM, then I realized what I had done wrong and I said, “Oh, I must have read the sticker wrong.” I think that the reduced price for the cake was around $10.00. I don't think that I had ever done that before. I felt very confused and not very smart, but the customer was very nice and understanding about the mix-up.