you could try using a uth? that will help maintain temps quite well if its regulated. The temperature drops slightly in my tank overnight because i use a heatlamp which is switched off. But my uth stays on continually so there is always a maintained hotspot.

Try not to worry yourself too much it has only been a week. Whenever i change my snakes tanks it usually takes a few days of adjustments and continually checking on temperatures to make sure everything is being maintained correctly. Every tank is different.