Zipadee zip

Does anyone have a zipadee zip? If so I'm curious about how snug it's supposed to fit around the neck. My LO doesn't seem to mind it but it fits snugly and it worries me a little. Does anyone else have this problem? I stretched it out when I put it on to make it a little bigger but now I'm nervous about it. Of course he went right to sleep just now without a problem. Idk if I should like wake him up and put him in his sleep sack. He's a skinny baby so it seems weird to me.