Hello!  Thank you for contacting Ask a Master Gardener with your questions about the Echibeckia Summerina Sunburst you recently planted.  Here's what I found for a possible cause:

Wilting can be a sign of either too little or too much moisture. If your plants are wilting, test the soil moisture and water deeply if soil is dry under 2” of soil for potted plants, and 6” for in-ground plants. If the soil is wet or soggy, allow it to dry before watering. Avoid the temptation to continue deeply watering, as overwatering further stresses plants. While a deep early-morning soaking can perk up a wilted plant experiencing heat stress, do not saturate it constantly to the point of waterlogging or you’ll have a whole new set of problems.

Wilting plants are a common sight in extreme heat. Many plants will wilt in the heat of the day and perk up in the evening as temperatures lower. If your plant remains wilted through the night, check your soil moisture levels.

It can take anywhere from a couple of days to a couple of months for stressed plants to recover. 

https://go.monrovia.com/help

Although tolerant of most soil types, it prefers to be grown in free-draining soil. Once established, this perennial is tolerant of dry conditions, but will need to be watered frequently after planting and for the first growing season. To support production of its eye-catching flowers, a slow-release, balanced fertilizer can be applied in spring.

https://plantaddicts.com/summerina-sunchaser-echibeckia

One other thing I noted is that you said you put 12-18" of topsoil in your flowerbed.  You may want to try using potting soil when transplanting and don't forget to untangle the roots as they are sometimes get bound up in the pots. Using potting soil in the hold softens up the dirt and allows the roots to establish easier.

I hope this helps you with your wilting Echibeckia problem.  Please write again if you have any further questions or concerns.

Happy gardening!

You're very welcome.  

We're always here to answer your gardening questions.

Hope you have a great summer!