Regret turning down a job offer

I was offered a job which I wasn't keen on taking after the interview as I lacked experience but waited a week to hear back and told I got the job. I was surprised because I couldn't answer all the questions well. But now I regret turning it down and wish I had just accepted. Has anyone ever turned down a job and realised it was a mistake and asked if it was still going?

P.s I haven't heard back from them for almost a week since I turned it down

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