Just double checking for safety reasons, since it sounds like you’re using a heat mat. This is on a thermostat with the probe between the mat and the enclosure (both on the outside of the enclosure), correct? How are you measuring the temps on the cool side?
As for the rest, you’ve found out why Snake Discovery and others warn about large enclosures with hogs. Yes, it technically can work if they are cluttered enough, but often times it doesn’t. You’ve already noticed the issue of not being able to easily see or check on him. This makes it harder to see any issues, symptoms of illness, and can make feeding more difficult. Hognoses are fossorial, so yes, they do love to burrow and feel safer underground, often staying out of sight for long periods.
Here’s a good guide by a breeder about baby Hoggies:
It may be beneficial to move him into a smaller enclosure until he’s grown up a bit, depending on how big the one you have now is.