It may be possible to still negotiate salary. It would help if you 'had another offer from a different company,' and they might pip it up a couple grand. But it seems to me like a very bad idea, and the tone of your message is that you have gotten greedy because you got the job easily and resoundingly.

If I was hiring and I heard that from you, I would not be happy, and I might decide that 'the company has put a hold on hiring' for the moment (a great way to avoid confrontation around rescinding an offer). In the best case, your first impression on your boss would be a bad one that they will never forget. First impressions are much more important than other impressions.

I would recommend you get in there and grind, and look at whether you are in a position to ask for a raise. Nobody knows whether you are going to do well in the job. If you "know" that you will, then this overconfidence -- which is the most common human bias -- is likely to bite you in the rear. Good luck.