Red mark on newborn??

Just noticed this little red mark on my little girl who is 17 days old, when she was 5 days old her cord fell off and I found it down the side of her sleepsuit I’m just wondering if that maybe dug into her side a little bit and I’ve only just noticed it now? If not what else could it be she doesn’t have anything in her bed to dig in, unless maybe when I’ve changed her one of the pop buttons on the vest dug in when i moved it?