Lol no they won't deny you for putting the wrong dates. If they verify the job and the dates are off they will just ask you about it and see if you were wrong on your dates or whatever but if you know you were wrong on your dates you can either let the person you in-processed with know that you put the wrong dates on PHQ, because I'm assuming you are in training still, or you can just wait for them to call you when the dates that you put don't match up with what the company verifies. (If they verifiy)
Either way nothing to worry about.