I can understand you being upset and unhappy. To be told you are getting one thing, and then get something else entirely is not a good experience.
My understanding is you did not get this snake from Ben, but from someone who claimed that they got it from Ben.
I would at least email and ask why the snake is so much smaller than what you were told, ask if it has problems eating.
For now, your baby is very stressed out, scared and unhappy. If you desire to keep it, then give it a week under optimal conditions to de-stress and unwind, and then try feeding again.
If you do decide to ask for a refund, remember to be as polite as possible. Just explain that you are concerned because the snake is much smaller than you thought it was going to be, and you are worried it might have issues eating. You may or may not get a refund, so be prepared to be turned down.
Gale