I dont think nothing's wrong.My phone stays in the low to mid 30's C range, but if I watch You Tube vids for about 20-30 minutes it will get around 42 C.
It kinda depends on outside temperature a little too.
Also the phone will shut down when it gets to hot as safety feature .I think it needs to get somewhere above 120 F to do that.
It usually cools down pretty quick afterwards.