It sounds like you are trying to use two very different methods for hibernating at the same time.
This is a BAD idea!
Get yourself a shovel, a small mountain of leaves, and maybe even a couple of small logs, then dig a hole in a spot in your yard that is not prone to flooding.
What has worked for me is to dig something of a trench (I dug down 2 ft., well below the frost line here), with a couple of sides that are sloped so that when spring comes, turts can climb out easily.
I then mixed in peat moss and lots of leaves with the soil (clay) that I'd dug out of the trench, and filled the hole back up with this loosened amended mixture (easier stuff for turts to dig in).For good measure I put a few inches of leaves on top of the amended soil, then put logs aross the trench, leaving the two sloping ends unobstructed. More leaves get piled over top of this. Turts hibernated successfully in central VA this way, with climate very similar to what you have in DE.
After mine emerged last spring, I checked the trench and found evidence that they had tunneled around quite a bit during the winter, and two tunnels went nearly to the bottom. They need to be able to move around quite a bit, in otherwords.
The sweater box method is for "artificial" hibernation in refridgeraters or garages, when turts are living outside their natural range, eg., and can't be hibernated naturally.
Putting the box in the ground is creating a potential coffin: please don't risk the chance of inadequate exchange of air, misjudging the appropriate depth to avoid frost, or the box filling with water and drowning your turtle.
Please get out there and take it out of that box ASAP!!
It sounds like you may just need to make a minor adjustment or two in order to correct the situation.
Once its out of that box, and in a good hibernaculum, it would probably be best to leave it alone and not check on it constantly: they have an innate ability to find the safest place to be, given the opportunity, and you may not be able to correctly duplicate those conditions, once disturbed.
Good luck!
Stephanie