Doyd, I agree with Ront, check the panel again. Also check the breaker sizes, unless the house was rewired (new wiring to receptacles and lights) they should all be 15A unless any new wire in the walls was added. A lot of homes in my area are of that vintage and a 30A was the norm. There is a possibility the service was upgraded. Like Bill said, a 100A with no major appliances is normally not a problem. Save your pennies and you can upgrade a little of the house at a time.
Rule of thumb,Keep your thumb from under the hammer!