turn off check engine light

You can try to disconnect the battery for a while and see if it will reset, if not, you need to take it to a repair shop to do it. Zee

It may reset by itself eventually, but if you have a mechanic friend, see if he'll clear it for you for free with his scanner (maybe bring him a sandwich). I would for something like that for my esteemed customers.

The light will go off after a day or two if the loose gas cap was indeed the reason for turning it on.