Here's a close up of the very corner. You can see where I graduated the stitches to accommodate the flowers. The second row, in the corner, started with a few single stitches, a few double stitches and several treble stitches then back to doubles, and singles. The third row was really short but using single stitches, doubles and then a single treble stitch in the corner squared the corner nicely.
Once the flowers were attached I eyed the arc of the mandala and used a stitch marker to show where I'd have to start building up with stitches to square up the corner. After I eyed the first marker placement, I counted from the marker to the first leaf and used that number to place more markers around the mandala for a total of eight markers.
I crocheted four white flowers that matched the flower ring and added one to each of the four corners where the markers were. Then I crocheted eight pink flowers from the center of the mandala pattern to put on either side of the white corner flowers.