Don't beat yourself up. The main thing is you're trying to make things right and coming to the right place to get the info you needPlease continue to ask questions and everyone will be more than happy to help!
You can always save your current hides for later whenever he gets bigger, or if you stuff them, a bp can never have too many hidesas long as he has two matching of the right size on each side.
Alternatively, here's an idea; once you get the appropriately sized hides you can use the big flat box one you have now as a "dig box" by flipping it upside down, fill with substrate and use that to place another hide over it so you can half bury it in substrate.