I agree with Floral that the bed is much too shallow and should be double what it is. While any perennial would fit when new, none will fit when grown and the size, even though we can't see the house, is surely not sufficient to be in scale with it. And I agree that the bulge makes no sense here.
A raised edging is a cheap looking way to border a bed. Instead, install a mowing strip which is flush with grade. The strip needs to be AT LEAST 8" thickness to be in scale with a lawn. 12" or even 16" works well, too. But a 2 1/2 or 6" thick paving strip looks underwhelming. Plain brick or pavers laid such that their long sides are abutting works well, since brick are 8" length, and is the most common.
Though it would not make as thick a border as necessary, the keystone block you have would be used like this...
The curve they make when oriented in the same direction is the curve you must use. Don't make it a wider curve with gaps at the joints. If will not look good if there are gaps. If you need a larger radius faceted circle, combine the blocks by placing two in one direction and one in opposite direction. (Still no gaps!)
And three in one direction plus one opposite will make an even larger faceted curve. In any case, there are never loose gaps at the joints. The blocks always abut each other tightly.
Q