I didn't use our electric blanket to heat me when I was pregnant, I used it to heat the bed. Once I got in, I would turn off the blanket. 102 degrees doesn't feel all that hot, so if you want to lie under an electric blanket that is turned on, take a thermometer and test in a few spots to see what temperature the blanket actually is when it feels "hot."
If i remember right they told me nothing 102f or higher... So i would think the blanket would be ok.
I would keep some space between your belly and blanket, but usually you can tell if its too much heat for your baby if it turns your skin red, which the blanket shouldn't be hot enough to do that.