Hi
If you're worried about the temperature of your mac I'd recommend the free trial of Temperature Gauge: https://www.tunabellysoftware.com/tgpro/
It tells you all of the temperatures inside your mac. Also when playing minecraft my macbook pro retina 13" CPU can get to 95 degrees celcius! also after a few hours the entire casing can be hot on bare skin if I keep playing. The macbook pro has a fan, the macbook 12" doesn't have a fan so its reasonable to expect it to become much hotter. If it becomes too hot it'll shut down.
If you get the temperature gauge, post what temps for the cpu or just a screenshot of the window like the one below of my mac. Im currently running Powerpoint, iTunes, mail, iMessage, calendar, iPhoto and obviously safari. Im also still on mavericks cause yosemite and el capitain aren't my preference in looks!
Anyway if people experiencing the excessive heat post screenshots of the temperature window and what their mac is running we can see if there are any that stand out and look abnormal.
I hope this helps 🙂