Why is my engine light on?

Honda accord 07 from dealership. Everything good but I got an oil change 4 days ago. Yesterday I had a thing come on the dash saying "check oil cap" I've read online about it saying that my filter might just need to be replaced by a Honda footer cause its tighter. I got an oil change from Walmart. Standard oil change. From 20% oil life to 100%. I'm not sure what to do. My engine light comes on now when i drive. Paid $42 for oil change. And they checked my lights and brakes and what not.

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