how not to sew a double felled seam
The two sections of this flag have been cut while the fabric was crooked. This has resulted in two distorted parts, and joining them has produced a curly seam. This has been made even worse by stretching the seam while sewing.

Sew Many Flags will show you how to avoid this type of mistakes.
Badly cut flag
This flag has also been cut crooked, not following the threads of the fabric. The result is a blunt corner and a distorted flag.