^^^ Well apart from people being able to buy more gas by simply driving more to burn up what they have - price caps will not cause a shortage if a real shortage doesn't exist.
Suppliers may create a false shortage by with holding supplies - but that would be counter productive in these crisis times.
Consumers do not have the ability to stockpile gas and store it so, apart from a few extra gallons people may buy with that extra gas can they have at home people won't suddenly buy 2000 gallons each
People could not "panic buy" more than their cars, weedwacker and lawnmoer could hold
This fact is born out by the many countries that have price control. Prices may not be the lowest, but it does not create instant shortages.
There are many instances where economic theory doesn't necessarily translate to economic text book practice.