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It is not likely to bloom its first year.
With proper care you should see increasing blooms next season.
The flowers are triggered in the fall as the light levels drop, not temperatures.

Here is a link with more information.
https://www.gardeningknowhow.com/ornamental/foliage/pampas-grass/growing-pampas-grass.htm

We cannot recommend specific retailers, but pampas grass seeds are available from many online gardening and landscape retailers, and may be available at gardening and hardware stores in your area.

Pampas grass should be planted in the spring, and I believe the purple variety is the same.

I am not sure what would cause this. Excessive nitrogen or possibly excessive heat can inhibit flower development, so perhaps they can inhibit plumes from fully developing and opening.

https://www.gardeningknowhow.com/ornamental/foliage/ornamental-grass/no-plumes-on-ornamental-grass.htm

Start your pampas grass seeds in spring, either indoors in containers or directly on the ground. Indoors, use a seed starting medium, and scatter the seeds on the surface of the soil. Keep them evenly moist until they germinate. Transplant to the desired outdoor location when they're about 5 inches high, and water them daily for the first week or so.

Outdoors, if you want the pampas grass to eventually grow in clumps, prepare areas of soil with compost about 8 feet apart from each other. Scatter some seeds on top of each patch of soil. Water the seeds daily until they begin to grow.

Vegetatively propagated (divided) clumps of Pampas grass can be transplanted in winter or early spring. If growing from seed, plant in the spring.