Any runners in the house?

[Nocturnal]

My foot often feels like it's not sitting completely on the shoe and when I feel it, I can feel it hanging off the side of the shoe. Is this going to hinder my running ability? I was told by the shoe salesman at Foot Action that the shoe would move with my foot lol. I know I'm stupid for believing him. Anyway, is this normal or should I look for a shoe that fits my entire foot without it hanging off the side?