Hi, and welcome to the site! I'm fairly new to ball pythons as well, but I'll help with what I can and hopefully someone else with more experience can help with the rest.
Ball pythons aren't really active snakes, and a hiding ball python is a happy ball python. That said, I'm a little concerned by the fact that you said that he's only a few days old - has he had any meals? It seems really odd that a pet store would sell a snake that young to a first time snake owner. You said the tank smells rotten. Was everything well cleaned when you put it in? Is it possible he's gone potty, and the tank needs to be cleaned?
What type of thermometer are you using? If it's a dial stick-on thermometer, they aren't very accurate. A digital thermometer with a probe, or a temp gun will be much more accurate. How are you measuring humidity? With a screen top, you'll probably need to cover a good portion (like 90%) of the top to keep the humidity where it needs to be (around 50-60%).
As BrandiR suggested, I would definitely get a thermostat is recommended to keep the heat pad from getting too hot and burning your snake. I would also try to get a night bulb instead of a bright bulb, because I think that would stress him to have a bright light on 24 hours a day. And I'm pretty sure you can just use a night bulb day and night, so no need for two separate bulbs.
Sorry, but I must have missed where you described his behavior? Unless you just meant him staying in the plants, which is just him being a ball python.
Hope that helps!