We just adopted a rehomed snake as well so congrats to you for giving this lil fella a new home!
I'd only add to all this good advice (that balled up newspaper trick is a sure winner btw) to maybe put his enclosure in a very quiet, reasonably low light area of your home, maybe like a bedroom or back room and then just leave it be other than changing water or removing waste for a good week or two. We have our rehome tucked in our bedroom (4 kids = noisy house) until we have a clear vet visit and a nice pattern of eating, pooping, peeing, shedding, etc.
Poor snake stuck in that box, no wonder it's striking and stressed. Did it have access to water those extra days? I'm sure with slow, steady steps you'll get this sweetie back on the right road.
Best of luck and welcome to this forum. It's a wonderful resource (and they don't seem to mind tons of questions either LOL)
~~Joanna~~