if the center finishes at 64, a 2.5 strip on each side will increase the size by 4", not just 2". AM I missing something?

You're right, it would increase it by 4" each way.


So instead of 2.5" border you'd need 1.5" border
which would then add 1" to top/bottom and each side resulting in a 66.5" unfinished center

Thanks everyone - I guess I have a choice...LOL Going to work on this in the morning and see what happens. Here is a sneak at one of the blocks that will be added after this border. Working at this backwards - I have the next border done before the one I can't figure out the size. Horse after the cart kind of thing.......... Some of you may remember me posting the WIP so you will know what quilt center it is being added to.