This is how I attached the border print and made the design flow uninterrupted around the ecge.  This works for patterns that are symmetrical, but would have to be modified for a border that didn't have mirror-image symmetry, like a floral vine or something.


I cut the printed border from both sides of the yardage, giving me two long strips.  I left a couple of repeats of the pattern and then formed the first corner, just pinning it at this stage.  ( Ideally there should be the same amount of fabric on either side, but I didn't have enough to do it that way.)

 I pinned the corner in place on the quilt, and measured the strip along the side of the quilt until I got to the next corner.  I made sure I had more fabric than I needed along the side , which meant going to the next repeat, and made the next  mitred corner.
I did this with both strips, so I had all the mitres pinned roughly. 

I didn't take proper pictures of the corners when I did the border, so I made a simple mitre from scraps to show how it's done.

To get a perfect mitre I marked a 45° line on the fabric, using an easily recognisable part of the pattern as my guide, so I could do all four corners the same.  In this case I used the centrre of the sunflower motif as an easy point of reference.

 I then marked a quarter inch line on the inner edge of the border, so I would know to stop my seam short of the seam allowance, which is the key to a successful mitre..

 I made sure the pattern on the underneath strip was lined up exactly with the one on top, and pinned in several places on the mitre line. I stitched all four mitres (backstitching at the inner edge to keep the stitching from coming undone later).  The extra fabric was trimmed off to give a quarter inch seam allowance.

That mitre looks pretty good to me..

To join it to the quilt, I made a dot a quarter inch in from both sides of the corner of the quilt.

I pinned the start of the mitre seam to this dot, and sewed the seam for a few inches.

 Then I sewed the other side, for a few inches only, again matching the start of the mitre seam to the dot.

 The reason I do this is because I want those corners joined correctly before I do anything else.  If I need to unpick and reposition, it's only a few inches that I have to rip out.

This is what it looks like on the back;

and from the front.

Once I had both corners joined, I pinned the first strip to the quilt working from each corner in towards the centre; as I got closer to the centre the excess fabric became apparent. 

Then I kept pinning carefully, until a pleat could be formed to take up the extra fabric.  I did this carefully to make sure the pattern was symmetrical either side of the pleat.

I unpinned it from the quilt, for about 10" either side of the pleat, and pressed the pleat to one side, so there was a  crease to follow as I stitched the seam.  The extra fabric is trimmed away and the seam pressed open.

 And there you have a border print that is perfect in the corners, and meets halfway forming a little joining pattern.
Add the other strip to the other long side, and then join the side borders in exactly the same way.  You'll be working with two strips on the side borders, instead of making a pleat you'll be forming a seam between the two strips, but the process is the same.

It's a simple thing to do, but awkward because you're working with all the quilt bundled in your lap or on the table, but the key is to take it slowly and carefully and the result is well worth it.