Received an Cambridge Offer - emailed US uni telling them

Hi,

I recvied an offer to read English Literature from University of Cambridge, as I don’t intent to go - but this still shows an added layer of verification, I emailed my top US uni letting them know, and I'm considering doing it for others, I was very polite and reaffirmed that they remain my top choice for X Y reasons and I only see the offer as evidence for my ability to thrive in the field ( due to the rigorous selection process) - but am now having second thoughts. Opinions ?