Did you marry within the 90 days given after entry on a K1 visa?
Did you include a copy of your marriage certificate with your original application?
From the letter, it looks to me they want to see a marriage certificate. I hope you didn’t send the original one and sent a certified copy as they will not return it back to you.
You won’t be deported. Worst case scenario is that you just refile a proper I-485 again.