LAF2019

I am working on a mystery quilt project that a guild member created. She gave the reveal a few weeks ago and I am almost finished.

The first picture shows the quilt center and the border (border is still in chunks and not yet fully pieced together and there is just one more seam to be sewn for the center piece). The border is obviously sized to fit the quilt center. However, I think it would look better with a thin inner border of my dark fabric (see second picture).

yes, the border goes all the way around the quilt, only my design wall is not big enough.

I know this additional inner border will change my needed dimensions for the outer border or it will not line up properly
How do I add in this little bit of extra border without interfering with the already planned border OR how do I adjust the outer border to accommodate the extra length/width?

I know i can make an additional "block" to the border construction, however that would force my new inner border to be too wide, I am really only wanting to add a thin 1/2 inch or 1 inch wide strip.

Any ideas or are there any math options? I certainly do not want to lose the points of triangles by appliqueing a thin piece on top of it once it's all done.

Thank you for looking!