05 Toyota Corolla Engine Light On 1 Day after Bought

#1
Hello y’all, on Saturday I bought a 2005 Toyota Corolla certified from a Used Mechanic/Dealership. It has 240000km on it and I have just driven around 800 km (driving around and I had bought it from a dealer a fair distance away). Then, on Sunday I wake up in my car only to find the engine light on after 1 day?!? To be honest with you guys, I did not screw my gas cap tightly which may be why and I screwed it back on. Yet after almost 100km it still is on. I don’t think I can go back to the dealer and complain as they are a few hundred kms away. Any help is appreciated TIA.
 
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