Get the code pulled thats setting the light off, then go from there.  The check engine light doesnt necessarily mean someting is wrong with your engine, just that something is wrong with your emissions system.  But yea, even a loose gas cap can set it off since your emissions system puts a vacuum in your tank to keep any fumes from getting out once you turn your car off.  If it can't pull a certain vacuum it will trip your light.  You can tighten your cap and reset the computer by unplugging your battery for 15 mins to try to get it to go away.

Thanks!