It's not apples to oranges. You ordered a WC gravid, and you should either get a WC gravid, or get your money back. But you want to keep the snake AND get your money back. That's the sticking point for me. Yes, he should have not made a mistake, but that's a moot point, you don't even know if it IS a mistake yet, just that it's likely a mistake.
You'll still get to aclimate a WC adult female, which can be dicey, even if you don't get eggs. I hope it lays for you. I hope you have good luck in getting the female to feed, and getting any viable hatchlings to feed.
Rarepythons is not exactly a great person to buy from, if that's who you got it from. If it does turn out to not be gravid, then you should be sure to contact him to ask for a full refund, and if he refuses, post on the BOI.