Mother of Christ why is everyone on this forum so utterly obsessed with perceived prestige which is, largely, peddled only on this forum anyway.
Look, the long and short of it is - you didn't apply, so you will never know. Having decided not to apply, you have secured an offer elsewhere. Now you are waivering because you think you are better than that and, therefore through logical extension, better than the people who are going to the university you have an offer at.
As I see it you have 2 choices, and it is only you who can decide. Either:
1) Accept you have a place at a uni that will give you a degree what will get you a job; or
2) Reapply next year after you have your results, include Kings in your application, and see where you go.
There is little point people going round in circles until you hear what it is you want to hear in order for you to justify to yourself taking option 2.