Hi. Glad to hear you have a new one your taking care of. It is really fun to get in this hobby. Looks like you are off to a good start but lets get a few things corrected. First do you have a thermostat to regulate the uth? that is very important as the uth can get very hot and burn your snake if it is uncontrolled. You can get a cheap one if you need off amazon for around $30 (hydrofarm). If you know anything about wiring you can try a stc-1000 off of ebay (i use this) which is around $10. Next you want to take the uth thermometer probe out of the tank and put it between the uth and the bottom of the glass:
Uth----> probe----->bottom tank not uth---->bottom tank---->probe
You want it this way because if water is spilled on it, the snake urinates on it or it gets moved your temp will be way off...you also want the tstat probe there too. For the hotspot you are going to want to bump that up to 88-90 which may be the reason that he is not feeding so well. 45% is a bit low for humidity so you might want to add some moss or cover the screen lid with plastic or foil (not the whole thing you need to get some airflow through)
Also for the heat lamp, is that an actual heat bulb or a daylight bulb? The daylight bulbs don't typically give off enough heat for the enclosure so replacing that with a CHE or actual heat bulb will help boost that ambient temp.
Another thing to consider is that tank you have for that size animal is huge! You will need to clutter it up more to give him more privacy. I would black out most of the tank (three sides) with some Black or dark colored paper to make is seem smaller. Also add hides and\or some fake plants and things to clutter it.
In the end you may end up having to get him something smaller till he grows a bit more. They really like small spaces. I have all mine started in 15qt tubs a few of them are pushing 500g in these with plenty of room.
The other thing is that you may just have a temperamental snake who is really picky about feeding. If that is the case there is nothing you can do but keep offering or trying to find another rodent he may like to eat. Maybe he will like rats better, its worth a shot.
Try these minute changes to your husbandry and see if he gets better. If not then hey thats just how he is. Good luck!!Please feel free to ask questions.