The lamp will turn off after a week of normal driving for most people.
Your car will need to run the evaporative system test 3 consecutive times
with no failures for the computer to turn off the lamp.  You should expect
that the test will run no more than once each time the vehicle is driven.  

turn you cap at least two to three full turns. The light should go out
within a week. Don't unscrew it and tighten it, won't work.
If it doesn't go out you can buy a new HYNDAI GAS CAP from your
dealer...NOT A STORE BOUGHT ONE.
As long as teh car isn't idleling rough or stalling, That would be a sign
of a bad oxygen sensor........... then it should be fine.
Nothing else should be wrong with your car other than teh gas cap.