The final assembly step is to put the final border on. It will be a 3" border, so cut 3.5" strips from the border fabric -- the fabric you had to have the most of.
The corner stones for the final border strips are the 3" friendship stars.
Adding your final 3" border brings it up to 52.5". With binding, maybe 53" now.
You will also be adding the binding which will be from the same border fabric as the final border.
And, as you've guessed, the applique portion goes in the center block.
That remains the final mystery.
(I have to figure out a way to upload it to everyone ...)
I hope everyone likes the Christmas/Winter mystery quilt so far.
I'll be back later to finalize the applique and solve the final mystery.