Basic question about why supply/demand should move to the equilibrium price?
What you write is true in a monopoly situation, but not when there are multiple firms on the supply side.

However, when equilibrium is discussed in this context people usually mean competitive equilibrium, that is equilibrium in a market where many firms compete. So at price \$1.80 several suppliers want to sell an aggregate amount of about 680 gallons. However demand is only 500 gallons. This would prompt the suppliers who are worried about not being able to unload all their stock to offer it at a slightly lower price, say \$1.79, undercutting their rivals' price. The idea is that by lowering the price somewhat you can greatly increase your market share, and unload your stock, to the general dissatisfaction of your rivals, who are now stuck with their own surplus gasoline.

Thus \$1.80 is not an equilibrium price, as suppliers have incentives to unilaterally push their own prices down.