Fell asleep with heating pad on! Help!

So I'm freaking out that I have just permanently harmed my baby. I'm 16 weeks pregnant and fell asleep with a heating pad on my upper back for about 4 hours! I also got overheated after coming out of the shower the other day because the heater was on and caused a sauna like effect in the bathroom. It's the weekened so I can't talk to my OB yet. I have my next appointment which will be 20 weeks in about a month. Will they be able to tell if the brain or anything has been effected? I keep reading that in the first trimester overheating can cause a miscarriage, effect Fetal brain development, and cause retardation. I'm not sure about what happens after the first trimester. I'm so worried that my stupid mistake has hurt my baby.