There is no such rigid rule as "cancellation" for the return of goods without quality problems. However, due to mistakes in the shopping mall, customers misunderstood and bought the wrong unpacked clothes, but they didn't wear them. Generally, shopping malls accept returns.

I don't know if you cut the rope of the clothes tag when you opened the bag, or if you removed the seam label from the clothes for the sake of beauty (this situation is more serious because it has nothing to do with the misunderstanding of size and the wrong packaging). In a word, if you open the package by mistake because of the shopping mall, you should argue it out. If the integrity of clothes is damaged due to other personal reasons, it should be resolved through consultation.