The budget for the film was very limited (around $800,000 total) but the director had no problems with this, as he was happy to work on a Roger Corman film and knew beforehand that Corman always kept expenses to a minimum.
Throughout the entire movie, people can be seen walking around in the background on different floors of the mall, even though it's supposed to be closed.
When the robot blows up the gas can in Suzie's hand, the only thing that burns is Suzie's body. The explosion should have sent burning fuel all over the place.