Legal Question in Consumer Law in Oregon

Legally, no. You contracted for X amount of gas and are not legally bound to pay for X+1 amount of gas.

If you use a credit card, then the answer is, practically, yes. The merchant can go ahead and charge your credit card for the full amount, and you will have to contest it. If you do not pay it, the merchant can file an adverse report with the credit rating agencies, which can negatively affect you in many ways.