BPs can be such derps sometimes! He should be fine (as long as the prey size is right). If he can't swallow it backwards he'll spit it out and get it facing the right way eventually. Mine did that once, coiled around the head and then couldn't find the head so he tried to eat it rear-end first for 20 minutesIn the end he let go of the mouse completely and finally found the head.
He also might be nervous, some BPs stop eating if you stare at them. It might help to just leave him alone in the dark so he can figure it out.