Hello and welcome!

So a few things

1. 40 gallon is too large for this little guy and he will feel a little insecure. to off set this you will need to fill the enclosure up with lots of stuff, really crown the space. (don’t worry about this too much, the snake will grow into the tank but many people will tell you its too large. if you clutter it things will be fine.
2. You need to try and set up a temperature granulation (hot and cool side with the middle be in-between). The 'hotspot' should be 87-91 degrees (that temp is off the floor of the cage, the snake will burrow down and you want to know what the temperature of the hottest place your snake could be in contact with. I recommend switching from the heat lamp to an under tank heater (UTH- heat pad). having belly heat helps with digestion and with this method it will be easier to control the hotspot in your set up. You will also need to purchase a thermostat that controls the heat pad and prevents it from getting too hot. You set the thermostat to lets say 93, measure the temp of the cage floor, and play around with it until you get a consistent 87-90.
3. Feeding: feed the little guy in his new set. Feeding them outside their cage does more harm than good. Make sure the prey is fully thaw (just a few min does not seem like enough time). After the pray is thawed hit the head and butt with a blow-dryer for a min (this dries the mouse off, and heats it up so the sent is stronger). use tongs or something similar when you offer, make the mouse do a little zombie dance if you need to. be patient. if he seems really interested, but does not strike, you can try leaving the mouse in with him for 20 min or so before checking. If he refuses again, wait 5 days before trying again.

Important things:
1. look up a care guide (there are lots on this site) to really nail down what your temps and humidity should be
2. get a simply heating pad and thermostat to regulate it

if you can post pictures of the set up that will also help to give some advice on the substrate, size of your hides, etc.
Congrats again, BP are the best!!