@Eunsang Hwang, this is not cut very well I'm afraid. The edges are not smooth, there's some snow, the dimensions aren't correct and there's too large a gap between the bottom of the chin and the bottom of the canvas.

Have a look at the guidelines and the video tutorials in this thread on how you can improve your cutting technique. I recommend using remove.bg and photopea, both free easy-to-use online tools which will provide you with excellent cuts in a quick timeframe 👍

Can you upload the source image so that we can attempt to re-cut this?