If it is anything like the Campanula persicifolia I have, "not enough sun" for flowering is near impossible and solidly contradicted by the photo. All the "volunteer" ones I had, started underneath thick cover of other weeds, in most cases even above those taller weeds was dense shade. So those campanula rosettes developed hidden and with near zero sunlight, but still managed throw stalks with flowers above the other weeds.
In one of two places I transplanted them into the open and then regularly watered, they did clearly better than where they volunteered. But in places where I just pulled the covering weeds and left campanula in place, they promptly died. So in my experience, full sun is something they tolerate if they are watered very regularly. But without such help, my campanula don't tolerate full sun, and do tolerate full shade.