some snakes wont eat unless its the right time of day, some wont eat unless its been long enough sense their last meal, while they store is open call them and find out when his last feeding was. you may have to leave the little rodent in there a while to get him to eat, if it is alive do not leave your snake and the food unattended. keep feeding tongs or a set of forceps handy if its alive or stunned to ensure if it tries to bite your animal you can stop it. your food item seems young but always better to be safe then have sorrow.
you also might want to wait a full week before trying to feed it, many snakes stress out from being moved and put in a new environment. a week to 2 weeks of leaving the snake alone and only checking water, humidity and temp are required to keep its stress down while it adjust to the new area its in. who did you buy him from that didn't give you this advise?