The completion effect is not good？

[learnuser1]

Is it because you still have some color remaining around the edges of your masked boundary? I have noticed a similar issue, and I found that applying dilation to the mask effectively resolves it by removing the residual colors.
input

mask

output

How can I fill in the missing hair area after removing a headpiece or accessory?

[zhangp365]

You can use an sd anime model to inpaint the area.