Service Engine Soon Light?!

As a former Certified Chrysler Warranty Admin. I OFTEN encountered this question. This one is easy. The fact that you stated that the light came on after getting gas, tells me that the cause of the light coming on is most likely due to an incorrectly replaced gas cap following the fill up. If the cap is not replaced correctly it sometimes doesn't form a complete seal and the vehicles PCM (powertrain control module) senses an evap leak and illuminates your check engine light. To avoid this from happening in future whenb replacing your gas cap following a fill up, be sure to turn cap and hear 3 clicks, that should be enough to ensure  a good tight seal. When I was a service department receptionist this was one of the most frequent complaints from owners and the reason we were trained when a customer complained of a check engine light the 1st question we we taught to ask was "Have you recently got gas"