Could leaving your car running while fueling.

Absolutely. You opened the gas cap with the ignition switch on and that set a diagnostic fault code for a "large evap. System leak". If the light doesn't turn off after turning the ignition switch off and back on, you'll have to have the code manually erased. If the light does turn off, the code will remain in memory for a while which could confuse a mechanic who might have to diagnose some totally different problem IF it develops.