Visualizing Electrical Potential
You have a fundamental misunderstanding about voltage. A voltage difference isn't caused by an imbalance in the amount of charge, it's caused by a difference in the amount of energy available from the charge.

As charge passes (i.e. current flows) through an incandescent lamp it loses electrical energy, which is converted to heat and light. The density of electrons is the same at both ends of the filament, but the charge entering the filament has more energy than the charge leaving the filament.