Dear ....,
I write to report a change that occurred to me over the past weekend. I had two interviews, including yours, back to back then. I had not expected to receive an officer from the other company but ultimately it did offer me, but later than yours. The other company never had any indication of its offer hence I had signed yours.
What attracted me more about the other company is the shorter commute. With gas prices being so unpredictable and I don't feel the price will go down any time soon, at least not during the summer months.
I would like to redact my acceptance immediately. I apologize for the inconvenience. It was a hard decision and I indeed struggled. But thought to share with you the change sooner than later.