I'm trying to make the pants of my character. I selected these vertex, used Looptools>Circle, rotated it and moved the selected circle to align with the reference, but when I delete the face it doesn't delete the whole thing and it looks off. What am I doing wrong? The last image is my goal.

I'm trying to make the pants of my character. I selected these vertex, used Looptools>Circle, rotated it and moved the selected circle to align with the reference, but when I delete the face it doesn't delete the whole thing and it looks off. What am I doing wrong? The last image is my goal.