The service engine light doesn't just come on because of the gas cap not being on tight. My service engine light had come on as well and I had it checked at the dealership. I no longer remember the error that tripped the light, but the dealer said that as long as it's a one time thing, it shouldn't be a problem and they reset the light.
Since then, it hasn't come on again. Considering you don't know what tripped the light, you're better off having it looked at sooner rather than later.
Since then, it hasn't come on again. Considering you don't know what tripped the light, you're better off having it looked at sooner rather than later.