Changing Fabric.com order?

Hello everyone!

So I was ordering fur for a commission today, and I thought I had enough white for the project. Turns out I don't! :( (This is why you check these things beforehand!) But I had literally JUST ordered fur from Fabric.com. Is there any way to add things to an order? It's still pending if that helps at all? Just wondering if anyone has had any experience with this. :(

Thanks!