Unfortunately that snake is severely under weight and obviously very ill - whether from a neurological defect, toxin, overheating, or other reason. If it's been holding that position for a while it could be nearing death, I have seen snakes in particular twist abnormally when they get close to the end. I don't want to scare you or make you feel like this is at all your fault - because it's not, this issue is the stores and the fact that they refuse to take responsibility for the health of the animals.
If it survives you can try and return it - but in all honesty if it is that bad off, they won't do much to fix her if they even can. Heat stroke will make this permanent, so will toxins, and if it can't eat it won't survive anyway. If the poor thing gets worse you may have to consider humane euthanasia.