Car engine light came on. Code reader came back PO456(leak Evap) and
PO353 (Coil) Screwed on the gas cap again. Now light has gone off. Runs okay. I guess I should still get it checked out

That is a soft code. Tightening the cap and running the car makes it go away. The sensor measures tank pressure. What car? PO353 is spark related, loose plug wire, spark module, coil pack. If it does it again, have someone look at it. .

2003 Toyota echo. Thanks

I would consider replacing the o-ring seal on the fuel cap (cheap and easy) and also replacing the affected coil pack since they are prone to failing over time.

Strange. Car runs tip top. After I tighten the gas cap

Tighten the gas cap: three clicks.
Filling the gas tank: one click.
Once the pump shuts of the first time, STOP PUMPING! Too much fuel forced in after that can severely damage critical and expensive emissions control components so please make it a habit of stopping at the first click.