Stars only have a curl in the corners?

Good afternoon! I took a picture of M27 – The Dumbbell Nebula last night:

Telescope: Bresser FirstLight MAK 100/1400 (an f/14 Maksutov)

Mount: Skywatcher HEQ-5 Pro SynScan GoTo

Camera: Canon EOS 1100D (unmodified)

Guiding system: –

In the center (e.g., the white dwarf), the stars are perfectly round, but in the corners, and not far from the center, the stars have a tail that always points toward the center of the image. I learned exactly that about coma, but I thought that in coma, the stars in the corners become lines. Can anyone help me? Best regards, Tjovo.