Symbol on car says to check engine?

i bought a 2007 chevy cobalt 3 weeks ago and the first day i got it i accidently put diesel gas. some people told me it will mess up the engine and i wouldnt be able to fix it. but i got the car fixed and it worked pretty good. and this morning i turned on my car and it was saying to check the engine. does that... show more i bought a 2007 chevy cobalt 3 weeks ago and the first day i got it i accidently put diesel gas. some people told me it will mess up the engine and i wouldnt be able to fix it. but i got the car fixed and it worked pretty good. and this morning i turned on my car and it was saying to check the engine. does that necessarily meen that theres somethng wrong with the engine for sure? what can i do so that sign will turn off?
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