Your definition of warm may not be the warm that would be ideal for him(choice wording). Pet stores honestly don't pay a lot of attention to their reptiles so I wouldn't be surprised if he wasn't given the proper size and just they assumed he was getting a certain size. If he's new to you, always wait a week. It's not a set rule but it's just something you do to let the snake settle in. I myself can vouch when I go places with new surroundings I am not as hungry as I am say if I'm at my house or my moms house and I know this is a stupid comparison but you should let your snake acclimate before feeding. Also being that it's a ball and they can get stressed easily at times, I would of fed something smaller then what's proper so that way you have a few good interactions with him, but again that's just my opinion. My main concern is if he did eat and he's not ideally kept what can happen with not being able to digest properly, and the issues that could happen because of that.
Honestly, please don't take this offensively because I mean it with the best intentions. The fact that you haven't gotten him properly set up, then tried to feed him that quickly after getting him both combined, but mainly the first one shows us that you honestly shouldn't keep that snake as a pet. The temperature of your room is not going to be in the mid-high 80's, much less the low 80's so I don't get how you would think he's warm enough?
This would be equal to me putting you in a cardboard box where you couldn't fully stretch out and put you on balled up news paper with a water bowl, have the temperatures in the 50's and give you a sweater and pants. Could you survive in that? Yes, but it's not the ideal conditions and you're not going to like it.