Marguerite daisy wilting

A week or so ago I bought 3 marguerite daisies. However in this time they all seem to be in the process of dying, and in various stages of decline. It has been hot, so I have watered a little bit regularly. The compost is moist, they’re in full sun for most of the day, but heard they can be fussy. I’ve also been deadheading the flower heads to encourage more blooms. However, clearly I’m doing something wrong? 2 are in pots and one is in the ground. Any advice? Or is there no hope?