First...it takes more than an hour to heat it up from the get go...so relax. Also a damp substate will take longer to heat but once heated will hold the temp longer.

Next how are you measuring the temp? Are you getting 75 at the probe site (under the hide) or up on the wall where I see the thermometer? Also, are you sure the thermostat and pad are working? Have you felt the bottom of the cage (below the substrate) to see if you can feel any heat?

Let me know on these and we will go from there.

Also, it was a really good idea to setup first and then bring your snake home as this will take a few days to get dialed in.