I'm 4wks pregnant.i sat real close to my heater last night..not even a foot & didn't realize my stomach got realhot and rashy-did i hurt the baby?

Possibly.: Erythema ab igne as you describe indicates that overnight you exposed your stomach to high temperatures - and heat is a known teratogen in the first trimester (especially spina bifida). Please take Folic Acid 1-4 mg daily and get an expert ultrasound at 11-13 weeks and at 18-20 weeks. Most of the time these one-time exposures are innocuous - so please do not repeat this, avoid all saunas.

Unlikely: The fetus is far from your skin, deep in your uterus. Heating of your skin would be passed throughout your bloodstream, slowly heating your body including your uterus. A person in a hot tub fights to elevate i their core body temp to 102F, as they feel extremely hot (not sick). Damage to a fetus occurs at 102 and above. So on awakening if you weren't feeling very hot, not to worry.